Article

Oceanic Boundary Conditions for Jakobshavn Glacier. Part II: Provenance and Sources of Variability of Disko Bay and Ilulissat Icefjord Waters, 1990–2011

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Abstract

Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. Basin waters in this fjord exchange with neighboring Disko Bay waters of a particular density at least once per year. This study determined the provenance of this isopycnic layer for 1990–2011 using hydrographic data from Cape Farewell to Baffin Bay. The warm Atlantic-origin core of the West Greenland Current never filled deep Disko Bay or entered the fjord basin because of bathymetric impediments on the west Greenland shelf. Instead, equal parts of Atlantic water and less-saline polar water filled the fjord basin and bathed Jakobshavn Glacier. The polar water fraction was often traceable to the East/West Greenland Current but sometimes to the colder Baffin Current. The huge annual temperature cycle on West Greenland Current isopycnals did not propagate into deep Disko Bay or the fjord basin because isopycnals over the west Greenland shelf were depressed during the warm autumn/winter phase of the cycle. Ilulissat Icefjord basin waters were anomalously cool in summer 2010. This was not because of the record low NAO index winter of 2009/10 or atmospheric anomalies over Baffin Bay but, possibly, because of high freshwater flux through the Canadian Arctic and a weak West Greenland Current in early 2010. Together, this caused cold Baffin Current water to flood the west Greenland shelf. Subpolar gyre warming associated with the NAO anomaly in winter 2009/10 was more likely responsible for the record warm Disko Bay and Ilulissat Icefjord basin waters of 2011/12.

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... Finally, there is the question of the ultimate origin of interannual temperature variability in DB/IIf. In a companion paper (Gladish et al. 2015), we address this question by examining hydrographic and meteorological data from the wider region. ...
... In fact, at essentially all frequencies WG1 150 m showed much greater temperature variability than DB 350 m (Fig. 8d). Some of the temperature variation at WG1 is associated with the wide range of potential densities (Table 4), but moorings at other depths in eastern Davis Strait show that a large annual cycle of temperature occurs in all WGC isopycnic layers that can connect to deep DB. Gladish et al. (2015) argues that the 300-m-deep Egedesminde Dyb Sill blocks the warmest WGC waters because those isopycnic layers migrate below the depth of this outer sill during the warm phase of the annual cycle. Virtual mooring Seals 300 m 2013 shows that IIf temperatures at 300 m varied over just a 0.368C interval from September 2012 until January 2013. ...
... This interface occupies various depths in DB but is often above or straddling the 200-m line (Fig. 3). Therefore, as Myers and Ribergaard (2013) suggested, the variability of waters shallower than 200 m (i.e., Polar Waters) in DB are a major, sometimes principle, source of variability for the thermal boundary condition of JG, despite the great depth of IIf (see also Gladish et al. 2015). ...
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Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8°C from 2009 to 2013, excluding 2010, when it was 1°C cooler. Despite this variability, summer potential densities in the basin were in the narrow range of 27.20 ≤ σ[subscript θ] ≤ 27.31 kg m[superscript −3], and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011–13 were therefore similar to those in 1998/99, when Jakobshavn Glacier began to retreat, while basin waters in 2010 were as cool as in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability. This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth.
... Recent studies have either focused on the hydrographic conditions on the coast or in fjords and their links to these changes. Few studies, however, have covered the links between the coastal system and fjords with marine-terminating glaciers (Carroll et al., 2018;Gladish et al., 2015;Mortensen et al., 2018;. Distinct seasonal hydrographic differences are observed between the coast and outer and inner fjords (Mortensen et al., 2018). ...
... To the latter the Oceans Melting Greenland program is underway with a larger data set covering the northwest and east coast. Consequently, a generally accepted nomenclature of water masses in the region is still missing, as is a thorough description of spatial water mass distribution on this scale (Addison, 1987;Bâcle et al., 2002;Curry et al., 2011;Gladish et al., 2015;Guéguen et al., 2014;Mortensen, 2015;Tomczak & Godfred, 2004). ...
... The majority of observations were collected within 1.5 month (10 June to 27 July 2016). By using a near-synoptic data set, we avoid the relatively large seasonal property variations, which have been observed by Curry et al. (2011) and Gladish et al. (2015) at discrete depths at a mooring section across Davis Strait at~67°N. This makes the interpretation of water masses and their distribution easier. ...
Article
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The accelerated melt of the Greenland Ice Sheet has been linked to a sudden increase in the presence of warm subsurface coastal water in west Greenland. Yet pathways of warm coastal water along the entire west Greenland coast have remained largely unstudied. Here we present the first, near‐synoptic hydrographic observations at both the continental slope and fjord entrances of the west Greenland coastal system from Cape Farewell (59°N) to Melville Bay (75°N) in summer 2016. We observed a distinct north‐south division in the water mass distribution in west Greenland, approximately partitioned by the northern part of Davis Strait, and a division between the continental slope and fjord entrances. Waters from the regional southern freshwater source with origin in the East Greenland Current that rounds Cape Farewell are not observed to enter Baffin Bay. The regional heat source transported by the west Greenland Current is blocked by Southwest Greenland Coastal Water in the south but the deep connections in the north allow warm deep Subpolar Mode Water to enter fjords. Furthermore, we observed cold and relative saline Baffin Bay Polar Water over the inner part of the banks, periodically reaching as far south as 64°N, suggesting the presence of an undescribed southward current at the Southwest Greenland continental shelf.
... However, the main source of Arctic water into Baffin Bay is through the three channels of the CAA: Nares Strait, Jones Sound, and Lancaster Sound [Tang et al., 2004;Curry et al., 2014]. The Arctic water entering through the CAA is colder than Arctic water in the WGC [Gladish et al., 2015]. ...
... It enters Baffin Bay as glacier melt and icebergs that break off the tongue of marine-terminating glaciers [Tang et al., 2004]. Typically, glaciers in Greenland end in jords which can be more than 800 m deep but have sill depths ranging from 150 to 250 m at the mouth of the jord [Johannessen et al., 2011;Myers and Ribergaard, 2013;Gladish et al., 2015]. The circulation within a jord is driven by the basal melting and subglacial discharge, and it is separated from the larger-scale circulation of Baffin Bay by the sill [Rignot et al., 2010;Straneo et al., 2010;Johannessen et al., 2011;Straneo and Heimbach, 2013;Gladish et al., 2015]. ...
... Typically, glaciers in Greenland end in jords which can be more than 800 m deep but have sill depths ranging from 150 to 250 m at the mouth of the jord [Johannessen et al., 2011;Myers and Ribergaard, 2013;Gladish et al., 2015]. The circulation within a jord is driven by the basal melting and subglacial discharge, and it is separated from the larger-scale circulation of Baffin Bay by the sill [Rignot et al., 2010;Straneo et al., 2010;Johannessen et al., 2011;Straneo and Heimbach, 2013;Gladish et al., 2015]. ...
Article
Greenland Ice Sheet meltwater runoff has been increasing in recent decades, especially in the southwest and the northeast. To determine the impact of this accelerating meltwater flux on Baffin Bay, we examine 8 numerical experiments using an ocean-sea-ice model: NEMO. Enhanced runoff causes shoreward-increasing sea surface height and strengthens the stratification in Baffin Bay. The changes in sea surface height reduces the southward transport through the Canadian Arctic Archipelago and strengthens the gyre circulation within Baffin Bay. The latter leads to further freshening of surface waters as it produces a larger northward surface freshwater transport across Davis Strait. Increasing the meltwater runoff leads to a warming and shallowing of the West Greenland Irminger Water on the northwest Greenland shelf. These warmer waters can now more easily enter fjords on the Greenland coast and thus provide additional heat to accelerate the melting of marine terminating glaciers.
... Along-fjord wind forcing has been shown to enhance estuarine (Moffat, 2014;Svendsen & Thompson, 1978) and subglacial circulation , with katabatic wind events allowing for roughly 10% of surface waters to be flushed out of the fjord (Spall et al., 2017). Dense coastal inflows are episodic gravity currents that can cascade over sills and renew basin waters (Edwards & Edelsten, 1977;Gladish, Holland, & Lee, 2015;Gladish, Holland, Rosing-Asvid, et al., 2015;Mortensen et al., 2014), typically lasting several months per event (Mortensen et al., 2011). Ultimately, assessing the influence of these disparate processes, which have distinct magnitudes and timing across the parameter space of Greenland fjords, is necessary in order to understand how offshore signals are transported to glacier termini. ...
... This subannual mode of basin renewal is similar to moored observations from Ilulissat Icefjord, west Greenland (69°N; Gladish, Holland, & Lee, 2015;Gladish, Holland, Rosing-Asvid, et al., 2015), where dense coastal inflows associated with rising coastal isopycnals cascade over the~250-m deep sill from winter to spring. Dense coastal inflows in Godthåbsfjord, located south of Davis Strait at 64°N, are generally more episodic (Mortensen et al., 2011). ...
... For fjords with shallow sills, such as Godthåbsfjord and Ilulissat Icefjord, we would expect shelf-forced intermediary and katabatic wind-driven circulation to be arrested (Spall et al., 2017), with hydrographic variability during nonsummer months driven by tidal mixing and dense coastal inflows (Gladish, Holland, Rosing-Asvid, et al., 2015;Mortensen et al., 2014). We note that compared to KS and Rink, seasonal inflow of the warmest WGIW waters into Ilulissat Icefjord is restricted offshore by the~300-m deep Egedesminde Dyb sill ( Figure 1a); here roughly equal parts of WGIW and AW fill the fjord basin during spring to summer (Gladish, Holland, & Lee, 2015). ...
Article
Greenland fjords provide a pathway for the inflow of warm shelf waters to glacier termini and outflow of glacially modified waters to the coastal ocean. Characterizing the dominant modes of variability in fjord circulation, and how they vary over subannual and seasonal time scales, is critical for predicting ocean heat transport to the ice. Here we present a 2-year hydrographic record from a suite of moorings in Davis Strait and two neighboring west Greenland fjords that exhibit contrasting fjord and glacier geometry (Kangerdlugssuaq Sermerssua and Rink Isbræ). Hydrographic variability above the sill exhibits clear seasonality, with a progressive cooling of near-surface waters and shoaling of deep isotherms above the sill during winter to spring. Renewal of below-sill waters coincides with the arrival of dense waters at the fjord mouth; warm, salty Atlantic-origin water cascades into fjord basins from winter to midsummer. We then use Seaglider observations at Davis Strait, along with reanalysis of sea ice and wind stress in Baffin Bay, to explore the role of the West Greenland Current and local air-sea forcing in driving fjord renewal. These results demonstrate the importance of both remote and local processes in driving renewal of near-terminus waters, highlighting the need for sustained observations and improved ocean models that resolve the complete slope-trough-fjord-ice system.
... We find that ocean temperatures in Disko Bay below about 150 m cooled by nearly 2 °C between 2014 and 2016. It is primarily water from this deeper layer that flows into Ilulissat Icefjord and comes into contact with Jakobshavn Isbrae at depth 25,26 . ...
... After flowing through Davis Strait at 67° N, a branch of the boundary current is steered northeast towards the ice sheet in a 350-m-deep trough cut into the shallower (100-250 m) continental shelf (Fig. 1b). This trough provides a pathway that permits warm, salty Atlantic Water to transit across the shelf beneath the shallower and fresher Polar Water layer 25,26 . Before reaching Jakobshavn, Atlantic Water in the trough is partially impeded by two sills, one at mid-shelf (68.50° ...
... A mixture of Atlantic and Polar waters with potential densities between 1,027.2 and 1,027.4 kg m −3 ( Supplementary Fig. 9) flows over this last sill into Ilulissat Icefjord 26 . Flushing of the fjord happens mostly during summer, when density surfaces are shallower and subglacial discharge ( Fig. 3c and Supplementary Fig. 16) drives strong circulation throughout the fjord 25 . ...
Article
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Jakobshavn Isbrae has been the single largest source of mass loss from the Greenland Ice Sheet over the last 20 years. During that time, it has been retreating, accelerating and thinning. Here we use airborne altimetry and satellite imagery to show that since 2016 Jakobshavn has been re-advancing, slowing and thickening. We link these changes to concurrent cooling of ocean waters in Disko Bay that spill over into Ilulissat Icefjord. Ocean temperatures in the bay’s upper 250 m have cooled to levels not seen since the mid 1980s. Observations and modelling trace the origins of this cooling to anomalous wintertime heat loss in the boundary current that circulates around the southern half of Greenland. Longer time series of ocean temperature, subglacial discharge and glacier variability strongly suggest that ocean-induced melting at the front has continued to influence glacier dynamics after the disintegration of its floating tongue in 2003. We conclude that projections of Jakobshavn’s future contribution to sea-level rise that are based on glacier geometry are insufficient, and that accounting for external forcing is indispensable. Jakobshavn Isbrae, the largest source of ice mass loss from the Greenland Ice Sheet, has been re-advancing since 2016 after a decades-long retreat, reveals an analysis of airborne altimetry and satellite data. The advance coincides with regional ocean cooling.
... Similar to previous short-term cooling events (Gladish et al., 2015a;2015b), and the warming of late the 1990s (Holland et al., 2008), Khazendar et al. (2019) showed that glacier retreat, ow acceleration and thinning were all strongly correlated with the temperature of ocean waters that come in contact with the glacier front. More speci cally, they found that glacier behavior was best explained by plume-driven melt rates at the glacier grounding line. ...
... Given that hydrographic conditions in the fjord can persist across several years (Gladish et al., 2015a), this gives us an opportunity to forecast the thinning and acceleration of Jakobshavn Isbrae for a year with warm water in the fjord and a range of typical subglacial discharge. Based on our analysis below, we predict a thinning of 11.4 ± 7.1 m year -1 between March 2020 and March 2021 within 5 -10 km of the front. ...
... Since 2009, eXpendable CTDs (XCTDs) have been used to survey the Ilulissat Icefjord. First presented in Gladish et al. (2015a), XCTD pro les were typically collected in June, July, or August, with 9 -12 pro les spaced along the length of the fjord, near the center line. Updated through 2018, these observations provide a recent time series of temperature and salinity within Ilulissat Icefjord. ...
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After three years of cold conditions, warm water has returned to Ilulissat Icefjord, home to Jakobshavn Isbrae—Greenland’s largest outlet glacier. Jakobshavn has slowed and thickened since 2016, when waters near the glacier cooled from 3 °C to 1.5 °C. Fjord temperatures remained cold through at least the end of 2019, but in March 2020, temperatures in the fjord warmed to 2.8 °C. As a result of the warming, we forecast that Jakobshavn Isbrae will accelerate and resume thinning during the 2020 melt season. The fjord’s profound influence on glacier behavior, and the connectivity between fjord conditions and regional ocean climate imply a degree of predictability that we aim to test with this forecast. Given the global importance of sea-level rise, we must advance our ability to forecast such rapidly changing systems, and this work represents an important first step in glacier forecasting.
... For these reasons, which might be summarised as problems of process understanding and scale, inclusion of ice sheet-ocean 5 processes in Greenland Ice Sheet models has proven difficult. A number of ad-hoc methods have therefore been used (Price et al., 2011;Goelzer et al., 2013;Nick et al., 2013;Fürst et al., 2015;Golledge et al., 2019), but such approaches often focus on large glaciers and rely on scaling arguments to obtain full ice sheet response, and/or are not faithful to the processes now believed to be responsible for terminus position change. ...
... Store Glacier has in contrast remained stable since at least 1970, with a very moderate retreat of a few hundred metres in the 1990s (Fig. 4f). Subglacial runoff has also increased steadily until the past few years (Fig. 4g) and ocean temperatures in CW 5 Greenland show an increasing trend throughout most of the period (Fig. 4h). Estimated variability in submarine melting ( Fig. 4i) explains only 29% of terminus position change (Fig. 4j). ...
... Through fjord dynamics and fjord-shelf exchange, thermal forcing at the calving front may differ from that on the continental shelf (e.g. Gladish et al., 2015a), and may differ at adjacent glaciers (Bartholomaus et al., 2016). There is therefore an urgent need for methods that can translate offshore ocean properties to calving front thermal forcing, and a pressing need for sustained 25 oceanographic observations with which to validate these models. ...
Article
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The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial runoff and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, runoff and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–present. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position and submarine melting and show that the proposed parameterisation has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low emissions RCP2.6 scenario. In contrast, a high emissions RCP8.5 scenario results in a median retreat of ∼6 km, with 35 % of glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.
... Disko Bay, western Greenland, is located at the southern border of the Arctic sea ice and is influenced by both sub-Arctic waters from southwestern Greenland and Arctic waters from Baffin Bay (Gladish et al. 2015), and all three Calanus species are generally abundant in the bay (Madsen et al. 2001;Swalethorp et al. 2011). Over the last three decades, Disko Bay has experienced a large decrease in sea ice cover, and also year-to-year variations have increased in the last decade (Hansen et al. 2006, The Greenland Ecosystem monitoring program, http://data.g-e-m. ...
... All three species overwinter at depth and the spring abundance of females therefore reflects the conditions for the population in the previous year and the inflow of water before the spring ascent. A potential explanation of the differences in contribution between the Arctic and North Atlantic Calanus females in Disko Bay and their different correlations with the physical parameters could be that they are carried by different water masses, that is, C. finmarchicus by the West Greenland Current, which flows northward along the coast of Greenland, and C. glacialis and C. hyperboreus by Baffin Bay water flowing in from the north/west (Gladish et al. 2015). The Baffin Bay water is typically colder that the AW, entailing a correlation between sea ice and the two Arctic Calanus species due to the influence of the Baffin Bay current on both. ...
... The Baffin Bay water is typically colder that the AW, entailing a correlation between sea ice and the two Arctic Calanus species due to the influence of the Baffin Bay current on both. Likewise, the west Greenland current carrying C. finmarchicus is typically warmer and therefore has a negative influence on the sea ice cover (Gladish et al. 2015). ...
Article
In a warmer Arctic with less sea ice and stronger stratification, the environmental changes are expected to impact the pelagic food web, but few biological studies supporting this exist compared with the well‐documented physical changes. Here, we analyze a subset of 13 yr of data from Disko Bay, Western Greenland, from the period 1992 to 2018 for trends in the key zooplankton genus Calanus during May and June in relation to physical conditions. In the 1990s, the small North Atlantic species Calanus finmarchicus and the two larger Arctic species Calanus hyperboreus and Calanus glacialis contributed equally to the copepod biomass. With the reduction in sea ice cover, however, the Arctic species have declined, and currently C. finmarchicus dominates the biomass. Because of the species shift, the Calanus community is now dominated by smaller individuals and the lipid content of Calanus females during spring and summer has decreased by 34%. Moreover, during the last decade the annual variation in population size has been prominent, Calanus virtually being absent in some years. Because of the central role of Calanus in the Arctic food web, the changes will likely impact higher trophic levels, including fish, sea birds, and marine mammals.
... Finally, regarding the ocean conditions, warm water temperatures in the fjord were recorded in 2012. Besides a cold anomaly in 2010, which was sustained until early 2011, the period 2008–2013 is characterized by high fjord water temperatures – equal to or warmer than those recorded in 1998– 1999 (Gladish et al., 2015a, b). In our model, the ice melt rates are determined from the given conditions in temperature (−1.7 @BULLET C and salinity (35 psu) of the fjord waters) and the given geometry (Sect. ...
... In our first experiment, the input T o was increased from −1.7 to −1 @BULLET C starting in 1997 (∼ 0.7 @BULLET C relative to 1990). This temperature increase is consistent with observed ocean temperatures at the mouth of the Ilulissat fjord (Gladish et al., 2015a, b) and generated in our simulation, for the period 1997–2014, an accelerated retreat of the front that does not correlate with observations (Fig. S7 ). Similarly, mass loss estimates from the simulations are significantly larger (by ∼ 50 %;Fig. ...
Article
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Observations over the past two decades show substantial ice loss associated with the speedup of marine terminating glaciers in Greenland. Here we use a regional 3-D outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in west Greenland. Using atmospheric and oceanic forcing we tune our model to reproduce the observed frontal changes of JI during 1990–2014. We identify two major accelerations. The first occurs in 1998, and is triggered by moderate thinning prior to 1998. The second acceleration, which starts in 2003 and peaks in summer 2004, is triggered by the final breakup of the floating tongue, which generates a reduction in buttressing at the JI terminus. This results in further thinning, and as the slope steepens inland, sustained high velocities have been observed at JI over the last decade. As opposed to other regions on the Greenland Ice Sheet (GrIS), where dynamically induced mass loss has slowed down over recent years, both modelled and observed results for JI suggest a continuation of the acceleration in mass loss. Further, we find that our model is not able to capture the 2012 peak in the observed velocities. Our analysis suggests that the 2012 acceleration of JI is likely the result of an exceptionally long melt season dominated by extreme melt events. Considering that such extreme surface melt events are expected to intensify in the future, our findings suggest that the 21st century projections of the GrIS mass loss and the future sea level rise may be larger than predicted by existing modelling results.
... The depths in the HighRes are about 400 m for MVBNT, and reaching almost 700 m depth for MVBCT and MVBST.Further south, on the west coast of Greenland, Jakobshavn Isbrae (JI) terminates into Disko Bay. The rapid retreat and disintegration of JI's floating ice tongue has been attributed to an increase in heat content, deep bathymetry, and NASPG30 warming(Holland et al., 2008;Myers and Ribergaard, 2013;Gladish et al., 2015;An et al., 2017). Recent slowing down of s acceleration has been attributed to the glacier reaching a higher bed, high amounts of freshwater from the Canadian Arctic, a weak WGC, or a cold Baffin Bay current flooding the West Greenland Shelf(Joughin et al., 2012;Gladish et al., 2015;An et al., 2017). ...
... The rapid retreat and disintegration of JI's floating ice tongue has been attributed to an increase in heat content, deep bathymetry, and NASPG30 warming(Holland et al., 2008;Myers and Ribergaard, 2013;Gladish et al., 2015;An et al., 2017). Recent slowing down of s acceleration has been attributed to the glacier reaching a higher bed, high amounts of freshwater from the Canadian Arctic, a weak WGC, or a cold Baffin Bay current flooding the West Greenland Shelf(Joughin et al., 2012;Gladish et al., 2015;An et al., 2017). In HighRes, the section drawn for Disko Bay(Fig. ...
Article
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The oceanic heat available in Greenland’s troughs is dependent on the location of the trough, the warm water origin, and how the water is impacted by local processes. This study investigates the mechanisms that bring warm water to the shelf and into the troughs abutting the Greenland Ice Sheet (GrIS). Warm water that is exchanged from the trough into the fjord may influence the melt on the marine terminating glaciers. Regional ocean model experiments showed that Melville Bay troughs experienced warming following 2009. An increase in ocean heat in these troughs may drive a retreat of the GrIS. In 2004 to 2006, model experiments captured an increase in onshore heat flux in the Disko Bay trough, coinciding with the timing of the disintegration of Jakobshavn Isbrae's floating tongue and observed ocean heat increase in Disko Bay. Warm Irminger water can extend far north into Baffin Bay, reaching as north as Melville Bay troughs. However, it diminishes north of 67° N on the east coast. Seasonality of the maximum onshore heat flux differs due to distance away from the original source. The north-west coast and south-east coast respond differently to changes in meltwater from Greenland and high frequency atmospheric phenomena. With a doubling of the GrIS meltwater, Baffin Bay troughs brought ∼40 % more heat. The lack of presence of storms resulted in an increase in heat flux (∼20 %) through Helheim glacier’s trough. These results demonstrate the importance of onshore heat transport through troughs and its potential implications to the GrIS.
... Further south, on the western coast of Greenland, Jakobshavn Isbrae (JI) terminates into Disko Bay. The rapid retreat and disintegration of JI's floating ice tongue have been attributed to an increase in heat content, deep bathymetry, and NASPG warming (Holland et al., 2008;Myers and Ribergaard, 2013;Gladish et al., 2015a;An et al., 2017). Recent slowing down of JI's acceleration has been attributed to the glacier reaching a higher bed, high amounts of freshwater from the Canadian Arctic, a weak WGC, or a cold Baffin Bay current flooding the West Greenland Shelf and cooling in the Labrador and Irminger Seas (Joughin et al., 2012;Gladish et al., 2015a;An et al., 2017;Khazendar et al., 2019). ...
... The rapid retreat and disintegration of JI's floating ice tongue have been attributed to an increase in heat content, deep bathymetry, and NASPG warming (Holland et al., 2008;Myers and Ribergaard, 2013;Gladish et al., 2015a;An et al., 2017). Recent slowing down of JI's acceleration has been attributed to the glacier reaching a higher bed, high amounts of freshwater from the Canadian Arctic, a weak WGC, or a cold Baffin Bay current flooding the West Greenland Shelf and cooling in the Labrador and Irminger Seas (Joughin et al., 2012;Gladish et al., 2015a;An et al., 2017;Khazendar et al., 2019). In HighRes, the section drawn for Disko Bay (Fig. 9b) shows two deep bathymetric features: the first trough, located at 100 to 200 km, and the second trough at 380 to 500 km, now called UT (Uummannaq trough) and DBT (Disko Bay trough), respectively. ...
Article
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The oceanic heat available in Greenland’s troughs is dependent on the geographic location of the trough, the water origin, and how the water is impacted by local processes along the pathway to the trough. This study investigates the spatial pattern and quantity of the warm water (with a temperature greater −1.5 ∘C) brought to the shelf and into the troughs abutting the Greenland Ice Sheet (GrIS). An increase in ocean heat in these troughs may drive a retreat of the GrIS. Warm water that is exchanged from the trough into the fjord may influence the melt on the marine-terminating glaciers. Several regional ocean model experiments were used to study regional differences in heat transport through troughs. Results showed that warm water extends north into Baffin Bay, reaching as far north as the Melville Bay troughs. Melville Bay troughs experienced warming following 2009. From 2004 to 2006, model experiments captured an increase in onshore heat flux in the Disko Bay trough, coinciding with the timing of the disintegration of Jakobshavn Isbrae's floating tongue and observed ocean heat increase in Disko Bay. The seasonality of the maximum onshore heat flux differs due to distance away from the Irminger Sea. Ocean temperatures near the northwestern coast and southeastern coast respond differently to changes in meltwater from Greenland and high-frequency atmospheric phenomena. With a doubling of the GrIS meltwater, Baffin Bay troughs transported ∼20 % more heat towards the coast. Fewer storms resulted in a doubling of onshore heat through Helheim Glacier's trough. These results demonstrate the regional variability of onshore heat transport through troughs and its potential implications to the GrIS.
... The global importance of Davis Strait relates to its role in transporting fresher, nutrient-rich and acidic water (Azetsu-Scott et al., 2010 toward the Labrador Sea where it may impact deep water formation and ecosystems along the coast of North America. The northward flowing WGC brings heat into Baffin Bay which has been linked to the rapid retreat of tidewaters glaciers in West Greenland (Gladish et al., 2015;Holland et al., 2008;Myers & Ribergaard, 2013;Straneo et al., 2012). ...
... The heat transport into Disko Bay also peaks earlier in the model timeseries, but only in summer, not in the winter. Gladish et al. (2015) also stated that in the summer of 2011, "warmer than ever" waters filled Disko Bay, as well as being observed on the West Greenland outer shelf. In the following two summers (2012 and 2013), Khazendar et al. (2019) reported the fastest flow speeds for Jacobshavn Isbrae, which is the tidewater glacier with Greenland's largest volume discharge, into Disko Bay. ...
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Plain Language Summary Baffin Bay exports cold and fresh Arctic Water to the North Atlantic while receiving northward flowing warm and saline Atlantic Water. This warm Atlantic Water has been shown to drive the retreat of tidewater glaciers. Periods of enhanced Atlantic Water transport into Baffin Bay have been observed. The oceanic processes that led to the enhanced transport of these warm waters into Baffin Bay are still not fully explained. Here we show from a combination of observational and model studies that at the end of 2010 the net transport at Davis Strait, the southern gateway to Baffin Bay, reversed from southward to northward for around a month, leading to significant northward oceanic heat transport into Baffin Bay. Anomalous winter winds kept the Atlantic Water on the West Greenland shelf, to propagate north into Baffin Bay instead of entering the interior Labrador Sea. At the same time, a mid‐level high pressure system sat over Greenland, efficiently preventing storms from reaching Baffin Bay. Anomalous winds also generated a positive transport signal that propagated cyclonically around Greenland, trapping warm waters on the West Greenland shelf, while also reversing the flow from the Arctic Ocean at Nares Strait.
... Between 2016 and 2017, it thickened by 20 to 30 m, and the measurements from 2018 confirm that its thickening continued at a similar rate. Scientists explain that the ocean temperatures have cooled by nearly 2°C in the vicinity of the glacier over the last several years (Gladish et al., 2015a;Gladish et al., 2015b). As a result, colder water is not melting the ice from the front and underneath the glacier as quickly as the warmer water did before. ...
... A recent study of comparison between ICESat and ICESat-2 data shows that in the period 2003-2019, the largest thinning is observed in the Jakobshavn glacier with values from 4 to 6 m yr −1 (Smith et al., 2020). However, taking into account only the last few years, studies show that from 2016 to 2018, Jakobshavn significantly thickened (Khazendar et al., 2019) due to the cooling of surrounding waters (Gladish et al., 2015a;Gladish et al., 2015b). We confirmed this fact for the upper part of the glacier. ...
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Ice-sheet mass balance and ice behaviour have been effectively monitored remotely by space-borne laser ranging technology, i.e. satellite laser altimetry, and/or satellite gravimetry. ICESat mission launched in 2003 has pioneered laser altimetry providing a large amount of elevation data related to ice sheet change with high spatial and temporal resolution. ICESat-2, the successor to the ICESat mission, was launched in 2018, continuing the legacy of its predecessor. This paper presents an overview of the satellite laser altimetry and a review of Greenland ice sheet change estimated from ICESat data and compared against estimates derived from satellite gravimetry, i.e. changes of the Earth's gravity field obtained from the GRACE data. In addition to that, it provides an insight into the characteristics and possibilities of ice sheet monitoring with renewed mission ICESat-2, which was compared against ICESat for the examination of ice height changes on the Jakobshavn glacier. ICESat comparison (2004-2008) shows that an average elevation change in different areas on Greenland varies up to ±0.60 m yr-1. Island's coastal southern regions are most affected by ice loss, while inland areas record near-balance state. In the same period, gravity anomaly measurements showed negative annual mass balance trends in coastal regions ranging from a few cm up to-0.36 m yr-1 w.e. (water equivalent), while inland records show slightly positive trends. According to GRACE observations, in the following years (2009-2017), negative annual mass balance trends on the coast continued.
... Whatever fraction of the late-winter Calanus population has arrived via the annual winter overturning of the deep layer (Gladish et al., 2015) is likely to have travelled hundreds or thousands of km (Figure 1) during that lag. We do not know what fraction of the population this is, but given that subarctic C. finmarchicus have increased in concert with the Atlantification of Disko Bay's physical water properties over the past decades (Møller and Nielsen, 2020), there is no reason to think that it is small. ...
... Diapause in copepods is usually explained in terms of three advantages that it confers: (i) reduction of energetic losses through partial metabolic shutdown, (ii) reduction of energetic losses through cold water temperature, and (iii) reduction of predation losses. Explanation (ii) does not apply in Disko Bay, because the influence of ice and the west Greenland current means that bottom water is not generally colder than surface water (Hansen et al., 2012;Gladish et al., 2015). Explanation (i) is more difficult to evaluate, but Swalethorp et al. (2011) found that all three species of Calanus in Disko Bay have ample storage lipids remaining at the end of winter (wax esters 35-70% of total body carbon in late March 2008). ...
Article
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Bowhead whales (Balaena mysticetus) visit Disko Bay, West Greenland in winter and early spring to feed on Calanus spp., at a time of year when the copepods are still mostly in diapause and concentrated in near-bottom patches. Combining past observations of copepod abundance and distribution with detailed observations of bowhead whale foraging behaviour from telemetry suggests that if the whales target the highest-density patches, they likely consume 26–75% of the Calanus standing stock annually. A parallel bioenergetic calculation further suggests that the whales' patch selection must be close to optimally efficient at finding hotspots of high density copepods near the sea floor in order for foraging in Disko Bay to be a net energetic gain. Annual Calanus consumption by bowhead whales is similar to median estimates of consumption by each of three zooplankton taxa (jellies, chaetognaths, and predatory copepods), and much greater than the median estimate of consumption by fish larvae, as derived from seasonal abundance and specific ingestion rates from the literature. The copepods' self-concentration during diapause, far from providing a refuge from predation, is the behaviour that makes this strong trophic link possible. Because the grazing impact of the whales comes 6–10 months later than the annual peak in primary production, and because Disko Bay sits at the end of rapid advective pathways (here delineated by a simple numerical particle-tracking experiment), it is likely that these Calanus populations act in part as a long-distance energetic bridge between the whales and primary production hundreds or thousands of km away.
... It is well established that rigid mélange is most prevalent during winter when surface air temperatures are low (Cassotto et al., 2015), which agrees with the results in Fig. 2. Nearby weather station data (Fig. 6) indicate that the 2016-2017 and 2017-2018 winters were moderately colder than normal for the decade but so was the 2014-2015 winter that was followed by a large summer speed-up, suggesting that air temperatures are not the only control on mélange rigidity. As noted above, 250 m water temperatures in Disko Bay were ∼ 1.5 • C cooler for 2016-2017 ( Fig. 6 and Khazendar et al., 2019), and this cold ocean layer should extend across the sill at the mouth of the fjord (Gladish et al., 2015a). A reasonable assumption is that this colder water facilitated the more rapid winter freeze-up and greater mélange rigidity throughout the winter of 2016-2017, with similar behaviour during subsequent winters. ...
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The speed of Greenland's fastest glacier, Jakobshavn Isbræ, has varied substantially since its speed-up in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speed-up and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 2016–2017 and 2017–2018, concurrent with terminus advances ∼6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean's dominant influence on Jakobshavn Isbræ is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations approach flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds were slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending.
... SW are a mixture of IIW and fresher, warmer waters originating from local freshwater sources and warmed by summer atmospheric forcing. IIW originates from Arctic Waters observed in Disko and Baffin Bays (Gladish et al., 2015b) that enter SF after crossing sills at the mouth of JI Fjord (Schumann et al., 2012), the confluence of JI Fjord and Tasiussaq Fjord (Gladish et al., 2015a), and the mouth of SF (Fig. 1). These summer fjord waters are observed in the outer SF by a set of far-field CTD profiles taken near the fjord mouth more than 10 km from the SS terminus (triangles in Fig. 7a). ...
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Measurements of near-ice (< 200 m) hydrography and near-terminus subglacial hydrology are lacking, due in large part to the difficulty in working at the margin of calving glaciers. Here we pair detailed hydrographic and bathymetric measurements collected with an autonomous underwater vehicle as close as 150 m from the ice–ocean interface of the Saqqarliup sermia–Sarqardleq Fjord system, West Greenland, with modeled and observed subglacial discharge locations and magnitudes. We find evidence of two main types of subsurface glacially modified water (GMW) with distinct properties and locations. The two GMW locations also align with modeled runoff discharged at separate locations along the grounded margin corresponding with two prominent subcatchments beneath Saqqarliup sermia. Thus, near-ice observations and subglacial discharge routing indicate that runoff from this glacier occurs primarily at two discrete locations and gives rise to two distinct glacially modified waters. Furthermore, we show that the location with the largest subglacial discharge is associated with the lighter, fresher glacially modified water mass. This is qualitatively consistent with results from an idealized plume model.
... Still, they need to feed to develop further, and the long spawning period of C. hyperboreus females increases the likelihood that some of the nauplii will match the bloom (Hirche, 2013). C. hyperboreus typically overwinters at temperatures from −1.8 to 3 • C (Gladish et al., 2015;Kjellerup et al., 2015;Visser et al., 2017). These temperature differences affect the lipid consumption during winter and the amount of lipid available for EP (Maps et al., 2013). ...
Article
Large, lipid-storing copepods play a central role in marine Arctic ecosystems. Knowledge of the mechanisms that control their oogenesis is important for understanding their phenology and population dynamics. We investigated the impact of female lipid content on the timing and cumulative egg production (EP) of Calanus hyperboreus at 0, 3 and 6◦C. The lipid content of females in early autumn was a good predictor of their EP potential. However, we saw no indication of a threshold in lipid content for initiation of spawning. Higher temperature resulted in 17 and 24 days earlier spawning at 3 and 6◦C compared with 0◦C, and the mean spawning duration was 8 and 30 days shorter, respectively. This illustrates that temperature affects the phenology of C. hyperboreus. When EP began, lipid metabolism increased 2–4 times. The females allocated 1.3 μg lipid per egg independent of temperature. However, the basic metabolism increased with increasing temperature; consequently, a smaller fraction of lipid was allocated for EP when the temperature increased.
... Thirdly, while we expect that our estimates of subglacial discharge Q entering the parameterization are accurate (e.g., Langen et al., 2015;Noël et al., 2018), the thermal forcing (TF) is highly simplified and thus less certain, being based on spatial and depth averaging of ocean temperatures over the continental shelf and beyond. Through fjord dynamics and fjord-shelf exchange, thermal forcing at the calving front may differ from that on the continental shelf (e.g., Gladish et al., 2015a) and may differ at adjacent glaciers . There is therefore an urgent need for methods that can translate offshore ocean properties to calving front thermal forcing and a pressing need for sustained oceanographic observations with which to validate these models. ...
Article
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The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice-sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial discharge and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, subglacial discharge and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–2018. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position change and submarine melting and show that the proposed parameterization has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered, suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low-emission RCP2.6 scenario. In contrast, a high-emission RCP8.5 scenario results in a median retreat of 4.2 km, with a quarter of tidewater glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice-sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.
... 2016 (Fig. 6 and Khazendar et al., 2019, and this cold ocean layer should extend across the sill at the mouth of the fjord(Gladish et al., 2015a). A reasonable assumption is that this colder water facilitated more rapid winter freeze up and greater mélange rigidity in the winter of 2016-17, with similar behavior the subsequent winters. ...
Article
Full-text available
The speed of Greenland’s fastest glacier, Jakobshavn Isbrae, has varied substantially since its speedup in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speedup and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 2016–17 and 2017–18, concurrent with terminus advances ~ 6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean’s dominant influence on Jakobshavn Isbrae is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations near flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds are slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending.
... SW are a mixture of IIW and fresher, warmer waters originating from local freshwater 15 sources and warmed by summer atmospheric forcing. IIW originates from Arctic Waters observed in Disko and Baffin Bays (Gladish et al., 2015b) that enter SF after crossing sills at the mouth of JI fjord (Schumann et al., 2012), the confluence of JI fjord and Tasiussaq fjord (Gladish et al., 2015a), and the mouth of SF (Fig. 1). These summer fjord waters are observed in the outer SF by a set of far-field CTD profiles taken near 20 the fjord mouth more than 10 km from the SS terminus (triangles in Fig. 7a). ...
Article
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Measurements of near-ice (< 200 m) hydrography and near-terminus subglacial hydrology are lacking due in large part to the difficulty in working at the margin of calving glaciers. Here we pair detailed hydrographic and bathymetric measurements collected with an Autonomous Underwater Vehicle as close as 150 m from the ice/ocean interface of the Sarqardliup sermia/Sarqardleq Fjord system, West Greenland, with modeled and observed subglacial discharge locations and magnitudes. We find evidence of two main types of subsurface glacially modified water localized in space and with distinct properties that are consistent with runoff discharged at two locations along the grounded margin. These locations, in turn, correspond with two prominent subglacial subcatchments beneath Sarqardliup sermia. Thus, near-ice observations and subglacial discharge routing indicate that subglacial discharge from this glacier occurs at only two primary locations and gives rise to two distinct glacially modified waters. Furthermore, we show that the location with the largest discharge flux is associated with the lighter, fresher glacially modified watermass. This is qualitatively consistent with results from an idealized plume model.
... BBPW is found over large parts of Baffin Bay (Figure 1a), occurring in a layer close to the surface in the eastern part near Greenland (e.g., Addison, 1987;Bâcle et al., 2002;Burgers et al., 2017;Mortensen, 2015;Randelhoff et al., 2019;Rysgaard et al., 2020), and in a layer located much deeper and below another water mass (in Davis Strait referred to as e.g., Arctic Water or Baffin Bay Arctic Water) in the western part close to Baffin Island (e.g., Bâcle et al., 2002;Burgers et al., 2017;Gladish et al., 2015;Lehmann et al., 2022;Randelhoff et al., 2019). The formation site of BBPW is still not known in detail. ...
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The waters on the West Greenland continental shelf and slope play an important role in the global climate system with their link to the subpolar North Atlantic Ocean circulation system and the Greenland Ice Sheet. Lately, low temperature waters on the West Greenland shelf have been observed as far south as ∼64°N and associated with a cold and relatively saline water mass originating north of Davis Strait in Baffin Bay referred to as Baffin Bay Polar Water (BBPW). Here we use long, seasonal hydrographic time series from West Greenland at ∼64°N to study how frequently BBPW is reaching this far south. The analysis covers the period 1950–2018 with a data gap between 1988 and 2005. BBPW was observed frequently and was responsible for the temperature changes observed in the late 1960s–1980s and more intermittently post‐2008. Some of the large temperature changes we observe in the time series have previously been ascribed to “Great Salinity Anomalies” (GSAs) propagating around the subpolar North Atlantic Ocean circulation system. The prevailing view of the propagation of GSAs has been ascribed to advection of anomalies along the large‐scale circulation system. Our study shows that BBPW may play an important role in the interpretation of GSAs and melt of the Greenland Ice Sheet. Large temporal temperature changes at ∼64°N are associated with arrival of BBPW from the north and not advection of anomalies with the large‐scale current system from the south. This advocates for a shift in water masses caused by changes in the position and/or strength of oceanic currents.
... The accelerated retreat of many tidewater outlet glaciers in Greenland has motivated recent fjord studies to assess the heat transport from relatively warm open ocean or coastal water masses to the tidewater outlet glaciers in the inner parts of fjords (Bendtsen et al., 2015;Mortensen et al., 2011;Motyka et al., 2011;Straneo et al., 2010;Sutherland & Straneo, 2012). Even though relatively warm open ocean water has been observed at entrances to tidewater outlet glacier fjords, little is known about water masses at fjord entrances and in the proximity of tidewater outlet glaciers, renewal rates, and their temporal connections with coastal water masses (e.g., Gladish et al., 2015;Jackson et al., 2014;Mortensen et al., 2013). One of the key questions is how hydrographic changes observed at the entrance of a fjord are transmitted through the fjord system to the glacier terminus . ...
Article
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Fjords form the gateway between the open ocean and the Greenland Ice Sheet (GIS) and consequently play a crucial role for the stability of the Ice Sheet. Hydrographic observations, especially with seasonal resolution, from these fjords are limited making it difficult to assess linkages between the fjord, coastal water masses and freshwater discharge from GIS. Here, we present a decade-long monthly hydrographic time series from a southwest Greenland fjord in direct contact with GIS. Our observations reveal significant temporal and spatial water mass variations related to coastal, glacial, and atmospheric dynamics. During winter, the fjord circulation is dominated by seasonal dense coastal inflows and the timing of these inflows determines intermediate and deep-water temperatures. During summer, runoff from GIS leads to a pronounced freshening of the fjord. In general, the fjord’s seasonal circulation system damps the seasonal variation in temperature in the fjord. This leads to a seasonal temperature range in the intermediate layer in the inner part of the fjord that is half the observed range at the fjord entrance. Changes in mean water temperatures in the intermediate layer seem predominantly linked to local coastal water masses, where cold winter/warm summer events decrease/increase the mean water temperatures. Consequently, these events play an important role in heat transport towards glacier termini.
... As such, the distribution and properties of GMW offer an integrated view of fjord circulation and ice-ocean interaction. Indeed, many studies of Greenland glacier-fjord systems use GMW characteristics either to infer circulation or reconstruct quantities such as submarine melt rates [Straneo et al., 2011Bartholomaus et al., 2013;Mortensen et al., 2013;Chauché et al., 2014;Inall et al., 2014;Gladish et al., 2015;Bendtsen et al., 2015]. Tracing GMW is particularly valuable for short surveys because energetic, nontidal, currents frequently alias synoptic velocity measurements, masking glacially driven circulations Jackson et al., 2014]. ...
Article
We present the first noble gas observations in a proglacial fjord in Greenland, providing an unprecedented view of surface and submarine melt pathways into the ocean. Using Optimum Multiparameter Analysis, noble gas concentrations remove large uncertainties inherent in previous studies of meltwater in Greenland fjords. We find glacially modified waters with submarine melt concentrations up to 0.66 ± 0.09% and runoff 3.9 ± 0.29%. Radiogenic enrichment of Helium enables identification of ice sheet near-bed melt (0.48 ± 0.08%). We identify distinct regions of meltwater export reflecting heterogeneous melt processes: a surface layer of both runoff and submarine melt and an intermediate layer composed primarily of submarine melt. Intermediate ocean waters carry the majority of heat to the fjords' glaciers, and warmer deep waters are isolated from the ice edge. The average entrainment ratio implies that ocean water masses are upwelled at a rate 30 times the combined glacial meltwater volume flux.
... Lower d 13 C values over time can be linked to a change in phytoplankton cell growth rate that could be interpreted as a decline in the photosynthetic rate and decrease in primary production in recent years (Laws et al. 1995;Burkhardt et al. 1999). Additionally, decreasing d 13 C values over time could also, in part, be attributed to the increased contribution of meltwater and associated input of terrestrial OM via glacial/surface runoff from the Jakobshavn Isbrae glacier to Disko Bay in recent years (Holland et al. 2008;Gladish et al. 2015). ...
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Climate change is causing physical and biological changes in the polar marine environment, which may impact higher trophic level predators such as the bowhead whale (Balaena mysticetus) and the structure of their food webs. We used bulk stable isotope analysis and compound-specific isotope analysis (CSIA) of individual amino acids (AA) to examine bowhead whale trophic position and the biogeochemistry of one of their feeding grounds, Disko Bay, West Greenland, over a period of 7 years (2007–2013). We also examined whether environmental conditions such as sea ice concentration and sea surface temperature were causing any interannual variation in isotope data. Bulk δ¹⁵N values were consistent across the 7 years of sampling and were similar between sex classes. Bulk δ¹³C and essential-AAs δ¹³C values displayed an overall temporal decline of 1.0 and 1.4‰, respectively. A significant positive linear relationship was found between δ¹³C of bulk skin and essential-AAs suggesting that some of the observed isotopic variation in bowhead whales between years reflect changes in the carbon at the base of the food web. There were no correlations between the δ¹³C and δ¹⁵N values of isotopic tracers with sea ice concentrations or sea surface temperatures. The trophic level of bowhead whales remained stable over time despite large interannual variability in ice and temperature regimes. Our results indicate that the recent environmental changes in West Greenland resulted in no trophic perturbation being transferred to bowhead whales during that time period. Our study shows that the novel approach of CSIA-AA can be used effectively to study the combined temporal variation of bowhead whale food web structure and ecosystem isotopic baseline values and detect changes at the species and ecosystem levels.
... Within each trough, temperatures of the mid-depth waters (~200 m) generally decrease by one-half to one degree from south to north and from the inner shelves toward the glaciers. Such cooling implies a modification of Atlantic Water during its transit with cooler neighboring waters, through both isopycnal mixing with Baffin Bay intermediate water (Gladish et al., 2015a) and diapycnal mixing with the overlying Polar Water near glacier fronts. ...
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Melting of the Greenland Ice Sheet represents a major uncertainty in projecting future rates of global sea-level rise. Much of this uncertainty is related to a lack of knowledge about subsurface ocean hydrographic properties, particularly heat content, how these properties are modified across the continental shelf, and the extent to which the ocean interacts with glaciers. Early results from NASA’s five-year Oceans Melting Greenland (OMG) mission, based on extensive hydrographic and bathymetric surveys, suggest that many glaciers terminate in deep water and are hence vulnerable to increased melting due to ocean-ice interaction. OMG will track ocean conditions and ice loss at glaciers around Greenland through the year 2020, providing critical information about ocean-driven Greenland ice mass loss in a warming climate.
Article
Cumberland Sound, host to a commercially viable fish population in the deepest depths, is a large embayment on the southeast coast of Baffin Island that opens to Davis Strait. Conductivity, temperature, and depth profiles were collected during three summer field seasons (2011–2013), and two moorings were deployed during 2011–2012. Within the sound, salinity increases with increasing depth while water temperature cools reaching a minimum of −1.49°C at roughly 100 m. Below 100 m, the water becomes both warmer and saltier. Temperature-salinity curves for each year followed a similar pattern, but the entire water column in Cumberland Sound cooled from 2011 to 2012, and then warmed through the summer of 2013. Even though the sound's maximum depth is over a kilometer deeper than its sill, water in the entire sound is well oxygenated. A comparison of water masses within the sound and in Davis Strait shows that, above the sill, the sound is flooded with cold Baffin Island Current water following an intermittent geostrophic flow pattern entering the sound along the north coast and leaving along the south. Below the sill, replenishment is infrequent and includes water from both the Baffin Island Current and the West Greenland Current. Deep water replenishment occurred more frequently on spring tides, especially in the fall of 2011. Although the sound's circulation is controlled by outside currents, internal water modifying processes occur such as estuarine flow and wind-driven mixing.
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Systematically monitoring Greenland's outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering four key outlet glaciers in Greenland: Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden, and Zachariæ Isstrøm. These data provide a new high temporal resolution record (6-day averaged solutions) of each glacier's evolution since 2014, and resolve recent seasonal speedup periods and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10 %. We find that since 2012, Jakobshavn Isbræ has been decelerating, and now flows approximately 1250 m yr−1 (10 %), slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant: up to 750 m yr−1 (14 %) at a distance of 12 km inland of the terminus. We also use our new dataset to estimate the duration of speedup periods (80–95 days) and to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbræ, with increases in speed of ∼ 1800 m yr−1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25 % (2015) and 18 % (2016) at Petermann Glacier and Zachariæ Isstrøm, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent and timely monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve.
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Observations over the past 2 decades show substantial ice loss associated with the speed-up of marineterminating glaciers in Greenland. Here we use a regional three-dimensional outlet glacier model to simulate the behaviour of Jakobshavn Isbræ (JI) located in western Greenland. Our approach is to model and understand the recent behaviour of JI with a physical process-based model. Using atmospheric forcing and an ocean parametrization we tune our model to reproduce observed frontal changes of JI during 1990-2014. In our simulations, most of the JI retreat during 1990-2014 is driven by the ocean parametrization used and the glacier's subsequent response, which is largely governed by bed geometry. In general, the study shows significant progress in modelling the temporal variability of the flow at JI. Our results suggest that the overall variability in modelled horizontal velocities is a response to variations in terminus position. The model simulates two major accelerations that are consistent with observations of changes in glacier terminus. The first event occurred in 1998 and was triggered by a retreat of the front and moderate thinning of JI prior to 1998. The second event, which started in 2003 and peaked in the summer 2004, was triggered by the final breakup of the floating tongue. This break-up reduced the buttressing at the JI terminus that resulted in further thinning. As the terminus retreated over a reverse bed slope into deeper water, sustained high velocities over the last decade have been observed at JI. Our model provides evidence that the 1998 and 2003 flow accelerations are most likely initiated by the ocean parametrization used but JI's subsequent dynamic response was governed by its own bed geometry. We are unable to reproduce the observed 2010-2012 terminus retreat in our simulations. We attribute this limitation to either inaccuracies in basal topography or to misrepresentations of the climatic forcings that were applied. Nevertheless, the model is able to simulate the previously observed increase in mass loss through 2014.
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Jakobshavn Isbræ, which terminates in Ilulissat Icefjord, has undergone rapid retreat and is currently the largest contributor to ice-sheet mass loss among Greenland's marine terminating glaciers. Accelerating mass loss is increasing fresh water discharge to the ocean, which can feed back on ice melt, impact marine ecosystems and potentially modify regional and larger scale ocean circulation. Here we present hydrographic observations, including inert geochemical tracers, that allow the first quantitative description of the glacially-modified waters exported from the Jakobshavn/Icefjord system. Observations within the fjord suggest a deep-reaching overturning cell driven by glacial buoyancy forcing. Modified waters containing submarine meltwater (up to 2.5 ± 0.12%), subglacial discharge (up to 6 ± 0.37%) and large portions of entrained ocean waters are seen to exit the fjord and flow north. The exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore.
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Abstract. Meltwater and sediment-laden plumes at tidewater glaciers, resulting from the localized subglacial discharge of surface melt, influence submarine melting of the glacier and the delivery of nutrients to the fjord's surface waters. It is usually assumed that increased subglacial discharge will promote the surfacing of these plumes. Here, at a west Greenland tidewater glacier, we investigate the counterintuitive observation of a non-surfacing plume in July 2012 (a year of record surface melting) compared to the surfacing of the plume in July 2013 (an average melt year). We combine oceanographic observations, subglacial discharge estimates and an idealized plume model to explain the observed plumes’ behavior and evaluate the relative impact of fjord stratification and subglacial discharge on plume dynamics. We find that increased fjord stratification prevented the plume from surfacing in 2012, show that the fjord was more stratified in 2012 due to increased freshwater content, and speculate that this arose from an accumulation of ice sheet surface meltwater in the fjord in this record melt year. By developing theoretical scalings, we show in general that fjord stratification exerts a dominant control on plume vertical extent (and thus surface expression), so that studies using plume surface expression as a means of diagnosing variability in glacial processes should account for possible changes in stratification. We introduce the idea that despite projections of increased surface melting over Greenland, the appearance of plumes at the fjord surface could in the future become less common if the increased freshwater acts to stratify fjords around the ice sheet. We discuss the implications of our findings for nutrient fluxes, trapping of atmospheric CO<sub>2</sub> and the properties of water exported from Greenland’s fjords.
Article
Glacier terminus changes are one of the hallmarks of worldwide glacier change, and thus, there is significant focus on the controls and limits to retreat in the literature. Here we use the observational record of glacier terminus change from satellite remote sensing data to characterize glacier retreat in central West Greenland with a focus on the last 30 years. We compare terminus observations of retreat to glacier/fjord geometry from available bed and bathymetry data and find that glacier retreat accelerates through wide, overdeepened parts of the bed characterized by retrograde bed slopes. We find that the morphology of the overdeepening can be used as a predictive measure for the length of retreat and that short regions (less than twice the seasonal change in terminus position) of the bed with prograde bed slopes are not sufficient to stop a retreating terminus. Even narrow overdeepenings can control glacier retreat, likely because they focus subglacial runoff, which entrains warm water in the fjords when it emerges at the grounding line and melts the terminus, creating enhanced local retreat. Future retreat of these glaciers is assessed given upstream fjord geometry.
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Meltwater and sediment-laden plumes at tidewater glaciers, resulting from the localized subglacial discharge of surface melt, influence submarine melting of the glacier and the delivery of nutrients to the fjord's surface waters. It is usually assumed that increased subglacial discharge will promote the surfacing of these plumes. Here, at a western Greenland tidewater glacier, we investigate the counterintuitive observation of a non-surfacing plume in July 2012 (a year of record surface melting) compared to the surfacing of the plume in July 2013 (an average melt year). We combine oceanographic observations, subglacial discharge estimates and an idealized plume model to explain the observed plumes' behavior and evaluate the relative impact of fjord stratification and subglacial discharge on plume dynamics. We find that increased fjord stratification prevented the plume from surfacing in 2012, show that the fjord was more stratified in 2012 due to increased freshwater content and speculate that this arose from an accumulation of ice sheet surface meltwater in the fjord in this record melt year. By developing theoretical scalings, we show that fjord stratification in general exerts a dominant control on plume vertical extent (and thus surface expression), so that studies using plume surface expression as a means of diagnosing variability in glacial processes should account for possible changes in stratification. We introduce the idea that, despite projections of increased surface melting over Greenland, the appearance of plumes at the fjord surface could in the future become less common if the increased freshwater acts to stratify fjords around the Greenland ice sheet. We discuss the implications of our findings for nutrient fluxes, trapping of atmospheric CO2 and the properties of water exported from Greenland's fjords.
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Mass loss from the Greenland ice sheet (GrIS) has increased over the last two decades in response to changes in global climate, motivating the scientific community to question how the GrIS will contribute to sea-level rise on timescales that are relevant to coastal communities. Observations also indicate that the impact of a melting GrIS extends beyond sea-level rise, including changes to ocean properties and circulation, nutrient and sediment cycling, and ecosystem function. Unfortunately, despite the rapid growth of interest in GrIS mass loss and its impacts, we still lack the ability to confidently predict the rate of future mass loss and the full impacts of this mass loss on the globe. Uncertainty in GrIS mass loss projections in part stems from the nonlinear response of the ice sheet to climate forcing, with many processes at play that influence how mass is lost. This is particularly true for outlet glaciers in Greenland that terminate in the ocean because their flow is strongly controlled by multiple processes that alter their boundary conditions at the ice-atmosphere, ice-ocean, and ice-bed interfaces. Many of these processes change on a range of overlapping timescales and are challenging to observe, making them difficult to understand and thus missing in prognostic ice sheet/climate models. For example, recent (beginning in the late 1990s) mass loss via outlet glaciers has been attributed primarily to changing ice-ocean interactions, driven by both oceanic and atmospheric warming, but the exact mechanisms controlling the onset of glacier retreat and the processes that regulate the amount of retreat remain uncertain. Here we review the progress in understanding GrIS outlet glacier sensitivity to climate change, how mass loss has changed over time, and how our understanding has evolved as observational capacity expanded. Although many processes are far better understood than they were even a decade ago, fundamental gaps in our understanding of certain processes remain. These gaps impede our ability to understand past changes in dynamics and to make more accurate mass loss projections under future climate change. As such, there is a pressing need for (1) improved, long-term observations at the ice-ocean and ice-bed boundaries, (2) more observationally constrained numerical ice flow models that are coupled to atmosphere and ocean models, and (3) continued development of a collaborative and interdisciplinary scientific community.
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The Greenland Ice Sheet is melting, and the rate of ice loss has increased 6-fold since the 1980s. At the same time, the Arctic sea ice extent is decreasing. Melt water runoff and sea ice reduction both influence light and nutrient availability in the coastal ocean with implications for the timing, distribution and magnitude of phytoplankton production. However, the integrated effect of both glacial and sea ice melt is highly variable in time and space, making it challenging to quantify. In this study, we evaluate the relative importance of these processes for the primary productivity of Disko Bay, West Greenland, one of the most important areas for biodiversity and fisheries around Greenland. We use a high-resolution 3D coupled hydrodynamic-biogeochemical model for 2004 to 2018 validated against in situ observations and remote sensing products. The model estimated net primary production (NPP) varied between 90–147 gC m-2 year-1 during 2004–2018, a period with variable freshwater discharges and sea ice cover. NPP correlated negatively with sea ice cover, and positively with freshwater discharge. Fresh water discharge had a strong local effect within ∼25 km of the source sustaining productive hot spot during summer. When considering the annual NPP at bay scale, sea ice cover was the most important controlling factor. In scenarios with no sea ice in spring, the model predicted ∼30 % increase in annual production compared to a situation with high sea ice cover. Our study indicates that decreasing ice cover and more freshwater discharge can work synergistically and will likely increase primary productivity of the coastal ocean around Greenland.
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Jakobshavn Glacier, west Greenland, has responded to temperature changes in Ilulissat Icefjord, into which it terminates. This study collected hydrographic observations inside Ilulissat Icefjord and from adjacent Disko Bay between 2001 and 2014. The warmest deep Disko Bay waters were blocked by the entrance sill and did not reach Jakobshavn Glacier. In the fjord basin, the summer mean temperature was 2.8°C from 2009 to 2013, excluding 2010, when it was 1°C cooler. Despite this variability, summer potential densities in the basin were in the narrow range of 27.20 ≤ σ[subscript θ] ≤ 27.31 kg m[superscript −3], and basin water properties matched those of Disko Bay in this layer each summer. This relation has likely held since at least 1980. Basin waters from 2009 and 2011–13 were therefore similar to those in 1998/99, when Jakobshavn Glacier began to retreat, while basin waters in 2010 were as cool as in the 1980s. The 2010 basin temperature anomaly was advected into Disko Bay, not produced by local atmospheric variability. This anomaly also shows that Ilulissat Icefjord basin waters were renewed annually or faster. Time series fragments inside the fjord did not capture the 2010 anomaly but show that the basin temperatures varied little subannually, outside of summer. Fjord velocity profiles from summer 2013 implied a basin renewal time scale of about 1 month. In model simulations of the fjord circulation, subglacial discharge from Jakobshavn Glacier could drive renewal of the fjord basin over a single summer, while baroclinic forcing from outside the fjord could not, because of the sill at the mouth.
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Atmospheric reanalyses depend on a mix of observations and model forecasts. In data-sparse regions such as the Arctic, the reanalysis solution is more dependent on the model structure, assumptions, and data assimilation methods than in data-rich regions. Applications such as the forcing of ice-ocean models are sensitive to the errors in reanalyses. Seven reanalysis datasets for the Arctic region are compared over the 30-yr period 1981-2010: National Centers for Environmental Prediction (NCEP)-National Center for Atmospheric Research Reanalysis 1 (NCEP-R1) and NCEP-U.S. Department of Energy Reanalysis 2 (NCEP-R2), Climate Forecast System Reanalysis (CFSR), Twentieth-Century Reanalysis (20CR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), ECMWF Interim Re-Analysis (ERA-Interim), and Japanese 25-year Reanalysis Project (JRA-25). Emphasis is placed on variables not observed directly including surface fluxes and precipitation and their trends. The monthly averaged surface temperatures, radiative fluxes, precipitation, and wind speed are compared to observed values to assess how well the reanalysis data solutions capture the seasonal cycles. Three models stand out as being more consistent with independent observations: CFSR, MERRA, and ERA-Interim. A coupled ice-ocean model is forced with four of the datasets to determine how estimates of the ice thickness compare to observed values for each forcing and how the total ice volume differs among the simulations. Significant differences in the correlation of the simulated ice thickness with submarine measurements were found, with the MERRA products giving the best correlation (R = 0.82). The trend in the total ice volume in September is greatest with MERRA (-4.1 x 10(3) km(3) decade(-1)) and least with CFSR (-2.7 x 10(3) km(3) decade(-1)).
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Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.
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Interaction of Greenland's marine-terminating glaciers with the ocean has emerged as a key term in the ice-sheet mass balance and a plausible trigger for their recent acceleration. Our knowledge of the dynamics, however, is limited by scarcity of ocean measurements at the glacier/ocean boundary. Here data collected near six marine-terminating glaciers (79 North, Kangerdlugssuaq, Helheim and Petermann glaciers, Jakobshavn Isbrae, and the combined Sermeq Kujatdleq and Akangnardleq) are compared to investigate the water masses and the circulation at the ice/ocean boundary. Polar Water, of Arctic origin, and Atlantic Water, from the subtropical North Atlantic, are found near all the glaciers. Property analysis indicates melting by Atlantic Water (AW; found at the grounding line depth near all the glaciers) and the influence of subglacial discharge at depth in summer. AW temperatures near the glaciers range from 4.58 8C in the southeast, to 0.168C in northwest Greenland, consistent with the distance from the subtropical North Atlantic and cooling across the continental shelf. A review of its offshore variability suggests that AW temperature changes in the fjords will be largest in southern and smallest in northwest Greenland, consistent with the regional distribution of the recent glacier acceleration.
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Aircraft laser-altimeter surveys in 1993 and 1998 over Kangerdlugssuaq Glacier in east Greenland reveal thinning, over the 5-year interim, of several meters for all surveyed areas within 70 km of the seaward ice front, rising to 50 meters in the final 5 km. Such rapid thinning is best explained by increased discharge velocities and associated creep thinning, most probably caused by enhanced lubrication of the glacier bed. The calving ice front over the past decade has occupied approximately the same location as in 1966. Velocity estimates for 1995/96 are about the same as those for 1966 and 1988, but significantly less than for 1999, suggesting that major thinning began after 1995.
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We examine the pattern of spreading of warm subtropical-origin waters around Greenland for the years 1992–2009 using a high-resolution (4 km horizontal grid) coupled ocean and sea-ice simulation. The simulation, provided by the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project, qualitatively reproduces the observed warming of subsurface waters in the subpolar gyre associated with changes of the North Atlantic atmospheric state that occurred in the mid-1990s. The modeled subsurface ocean temperature warmed by 1.5°C in southeast and southwest Greenland during 1994–2005 and subsequently cooled by 0.5°C; modeled subsurface ocean temperature increased by 2–2.5°C in central and then northwest Greenland during 1997–2005 and stabilized thereafter, while it increased after 2005 by
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Photogrammetric reanalysis of 1985 aerial photos has revealed substantial submarine melting of the floating ice tongue of Jakobshavn Isbræ, west Greenland. The thickness of the floating tongue determined from hydrostatic equilibrium tapers from ∼940 m near the grounding zone to ∼600 m near the terminus. Feature tracking on orthophotos shows speeds on the July 1985 ice tongue to be nearly constant (∼18.5 m d−1), indicating negligible dynamic thinning. The thinning of the ice tongue is mostly due to submarine melting with average rates of 228 ± 49 m yr−1 (0.62 ± 0.13 m d−1) between the summers of 1984 and 1985. The cause of the high melt rate is the circulation of warm seawater (thermal forcing of up to 4.2°C) beneath the tongue with convection driven by the substantial discharge of subglacial freshwater from the grounding zone. We believe that this buoyancy-driven convection is responsible for a deep channel incised into the sole of the floating tongue. A dramatic thinning, retreat, and speedup began in 1998 and continues today. The timing of the change is coincident with a 1.1°C warming of deep ocean waters entering the fjord after 1997. Assuming a linear relationship between thermal forcing and submarine melt rate, average melt rates should have increased by ∼25% (∼57 m yr−1), sufficient to destabilize the ice tongue and initiate the ice thinning and the retreat that followed.
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Acceleration of Greenland's three largest outlet glaciers, Helheim, Kangerdlugssuaq and Jakobshavn Isbr, accounted for a substantial portion of the ice sheet's mass loss over the past decade. Rapid changes in their discharge, however, make their cumulative mass-change uncertain. We derive monthly mass balance rates and cumulative balance from discharge and surface mass balance (SMB) rates for these glaciers from 2000 through 2010. Despite the dramatic changes observed at Helheim, the glacier gained mass over the period, due primarily to the short-duration of acceleration and a likely longer-term positive balance. In contrast, Jakobshavn Isbr lost an equivalent of over 11 times the average annual SMB and loss continues to accelerate. Kangerdlugssuaq lost over 7 times its annual average SMB, but loss has returned to the 2000 rate. These differences point to contrasts in the long-term evolution of these glaciers and the danger in basing predictions on extrapolations of recent changes.
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Observations over the past decades show a rapid acceleration of several outlet glaciers in Greenland and Antarctica. One of the largest changes is a sudden switch of Jakobshavn Isbræ, a large outlet glacier feeding a deep-ocean fjord on Greenland's west coast, from slow thickening to rapid thinning in 1997, associated with a doubling in glacier velocity. Suggested explanations for the speed-up of Jakobshavn Isbræ include increased lubrication of the ice-bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers and weakening and break-up of the floating ice tongue that buttressed the glacier. Here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbræ were instead triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland. We trace these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. We conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets.
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The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from similar to 6% in Version 2.0 to similar to 11% in Version 3.0. Citation: Jakobsson, M., et al. (2012), The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0, Geophys. Res. Lett., 39, L12609, doi:10.1029/2012GL052219.
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Jakobshavn Isbrae is the most active glacier in Greenland, with an annual discharge of about 30 km3 of ice, and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998, despite locally warm summers. Repeated airborne laser-altimeter surveys along a 120 km profile in the glacier basin show slow, sporadic thickening between 1991 and 1997, suggesting a small positive mass balance, but since 1997 there has been sustained thinning of several m a-1 within 20 km of the ice front, with lower rates of thinning further inland. Here, we use weather-station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates, and thus to infer the temporal and spatial patterns of dynamic thinning. These show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning, initially confined to the lower reaches of the glacier (below about 500 m elevation), but progressively spreading inland until, between 1999 and 2001, thinning predominated over the entire surveyed region, up to 2000 m elevation. If this continues, the glacier calving front and probably its grounding line will retreat substantially in the very near future.
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Comparisons are made between a time series of meteorological surface layer observational data taken on board the R/V Knorr, and model analysis data from the European Centre for Medium-Range Weather Forecasting (ECMWF) and the National Centers for Environmental Prediction (NCEP). The observational data were gathered during a winter cruise of the R/V Knorr, from 6 February to 13 March 1997, as part of the Labrador Sea Deep Convection Experiment. The surface layer observations generally compare well with both model representations of the wintertime atmosphere. The biases that exist are mainly related to discrepancies in the sea surface temperature or the relative humidity of the analyses. The surface layer observations are used to generate bulk estimates of the surface momentum flux, and the surface sensible and latent heat fluxes. These are then compared with the model-generated turbulent surface fluxes. The ECMWF surface sensible and latent heat flux time series compare reasonably well, with overestimates of only 13% and 10%, respectively. In contrast, the NCEP model overestimates the bulk fluxes by 51% and 27%, respectively. The differences between the bulk estimates and those of the two models are due to different surface heat flux algorithms. It is shown that the roughness length formula used in the NCEP reanalysis project is inappropriate for moderate to high wind speeds. Its failings are acute for situations of large air–sea temperature difference and high wind speed, that is, for areas of high sensible heat fluxes such as the Labrador Sea, the Norwegian Sea, the Gulf Stream, and the Kuroshio. The new operational NCEP bulk algorithm is found to be more appropriate for such areas. It is concluded that surface turbulent flux fields from the ECMWF are within the bounds of observational uncertainty and therefore suitable for driving ocean models. This is in contrast to the surface flux fields from the NCEP reanalysis project, where the application of a more suitable algorithm to the model surface-layer meteorological data is recommended.
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ERA-Interim is the latest global atmospheric reanalysis produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). The ERA-Interim project was conducted in part to prepare for a new atmospheric reanalysis to replace ERA-40, which will extend back to the early part of the twentieth century. This article describes the forecast model, data assimilation method, and input datasets used to produce ERA-Interim, and discusses the performance of the system. Special emphasis is placed on various difficulties encountered in the production of ERA-40, including the representation of the hydrological cycle, the quality of the stratospheric circulation, and the consistency in time of the reanalysed fields. We provide evidence for substantial improvements in each of these aspects. We also identify areas where further work is needed and describe opportunities and objectives for future reanalysis projects at ECMWF.
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A significant amount of the measured coastal thinning of the Greenland ice sheet may be due to recent acceleration of outlet glaciers. Using remote sensing, we measured two major periods of speedup on Helheim Glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km/yr. These speedups coincided with rapid retreats of the calving front, totaling over 7.5 km. The glacier also thinned by over 40 m from 2001 to 2003. Retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area. Farther up-glacier, acceleration may be a delayed response to surface draw-down and steepening of the glacier's main trunk. If the 2005 speedup also produces strong thinning, then much of the glacier's main trunk may un-ground, leading to further retreat. [1] A significant amount of the measured coastal thinning of the Greenland ice sheet may be due to recent acceleration of outlet glaciers. Using remote sensing, we measured two major periods of speedup on Helheim Glacier between 2000 and 2005 that increased peak speeds from approximately 8 to 11 km/yr. These speedups coincided with rapid retreats of the calving front, totaling over 7.5 km. The glacier also thinned by over 40 m from 2001 to 2003. Retreat of the ice front appears to decrease resistance to flow and concentrates the gravitational driving force over a smaller area. Farther up-glacier, acceleration may be a delayed response to surface draw-down and steepening of the glacier's main trunk. If the 2005 speedup also produces strong thinning, then much of the glacier's main trunk may un-ground, leading to further retreat.
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In 1979, the General Bathymetric Chart of the Oceans (GEBCO) published Sheet 5.17 in the Fifth Edition of its series of global bathymetric maps. Sheet 5.17 covered the northern polar region above 64° N, and was for long the authoritative portrayal of Arctic bathymetry. The GEBCO compilation team had access to an extremely sparse sounding database from the central Arctic Ocean, due to the difficulty of mapping in this permanently ice covered region. In the past decade, there has been a substantial increase in the database of central Arctic Ocean bathymetry, due to the declassification of sounding data collected by US and British Navy nuclear submarines, and to the capability of modern icebreakers to measure ocean depths in heavy ice conditions. From these data sets, evidence has mounted to indicate that many of the smaller (and some larger) bathymetric features of Sheet 5.17 were poorly or wrongly defined. Within the framework of the project to construct the International Bathymetric Chart of the Arctic Ocean (IBCAO), all available historic and modern data sets were compiled to create a digital bathymetric model. In this paper, we compare both generally and in detail the contents of GEBCO Sheet 5.17 and version 1.0 of IBCAO, two bathymetric portrayals that were created more than 20years apart. The results should be helpful in the analysis and assessment of previously published studies that were based on GEBCO Sheet 5.17.
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Repeated laser-altimeter surveys and modelled snowfall/summer melt show average ice loss from Greenland between 1997 and 2003 was 80 ± 12 km3 yr, compared to about 60 km3 yr 1 for 1993/4–1998/9. Half of the increase was from higher summer melting, with the rest caused by velocities of some glaciers exceeding those needed to balance upstream snow accumulation. Velocities of one large glacier almost doubled between 1997 and 2003, resulting in net loss from its drainage basin by about 20 km of ice between 2002 and 2003.
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High-resolution hydrographic and velocity measurements across the East Greenland shelf break south of Denmark Strait have revealed an intense, narrow current banked against the upper continental slope. This is believed to be the result of dense water cascading over the shelf edge and entraining ambient water. The current has been named the East Greenland Spill Jet. It resides beneath the East Greenland/Irminger Current and transports roughly 2 Sverdrups of water equatorward. Strong vertical mixing occurs during the spilling, although the entrainment farther downstream is minimal. A vorticity analysis reveals that the increase in cyclonic relative vorticity within the jet is partly balanced by tilting vorticity, resulting in a sharp front in potential vorticity reminiscent of the Gulf Stream. The other components of the Irminger Sea boundary current system are described, including a presentation of absolute transports. Author Posting. © American Meteorological Society, 2005. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 35 (2005): 1037-1053, doi:10.1175/JPO2734.1. This project was funded by the National Science Foundation under Grant OCE 00-02492.
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Using satellite radar interferometry observations of Greenland, we detected widespread glacier acceleration below 66° north between 1996 and 2000, which rapidly expanded to 70° north in 2005. Accelerated ice discharge in the west and particularly in the east doubled the ice sheet mass deficit in the last decade from 90 to 220 cubic kilometers per year. As more glaciers accelerate farther north, the contribution of Greenland to sea-level rise will continue to increase.
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Greenland ice-core data have revealed large decadal climate variations over the North Atlantic that can be related to a major source of low-frequency variability, the North Atlantic Oscillation. Over the past decade, the Oscillation has remained in one extreme phase during the winters, contributing significantly to the recent wintertime warmth across Europe and to cold conditions in the northwest Atlantic. An evaluation of the atmospheric moisture budget reveals coherent large-scale changes since 1980 that are linked to recent dry conditions over southern Europe and the Mediterranean, whereas northern Europe and parts of Scandinavia have generally experienced wetter than normal conditions.
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Data on bathymetry, temperature, salinity and currents up to and including 1975 are used in describing the seasonal changes and dynamics of the hydrography of Disko Bugt, the Vaigat and adjacent glacier and non glacier fjords. An extensive upwelling of W Greenland water occurs in the northern part of the bay during the summer and fall and similar phenomena occur in Disko Fjord.-from Author
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Davis Strait is a primary gateway for freshwater exchange between the Arctic and North Atlantic Oceans including freshwater contributions from west Greenland and Canadian Arctic Archipelago glacial melt. Data from six years (2004-10) of continuous measurements collected by a full-strait moored array and concurrent high-resolution Seaglider surveys are used to estimate volume and liquid freshwater transports through Davis Strait, with respective annual averages of -1.6 +/- 0.5 Sverdrups (Sv; 1 Sv equivalent to 10(6) m(3) s(-1)) and -93 +/- 6 mSv (negative sign indicates southward transport). Sea ice export contributes an additional -10 +/- 1 mSv of freshwater transport, estimated using satellite ice area transport and moored upward-looking sonar ice thickness measurements. Interannual and annual variability of the net transports are large, with average annual volume and liquid freshwater transport standard deviations of 0.7 Sv and 17 mSv and with interannual standard deviations of 0.3 Sv and 15 mSv. Moreover, there are no clear trends in the net transports over the 6-yr period. However, salinity in the upper 250 m between Baffin Island and midstrait decreases starting in September 2009 and remains below average through August 2010, but appears to return to normal by the end of 2010. This freshening event, likely caused by changes in arctic freshwater storage, is not apparent in the liquid freshwater transport time series due to a reduction in southward volume transport in 2009-10. Reanalysis of Davis Strait mooring data from the period 1987-90, compared to the 2004-10 measurements, reveals less arctic outflow and warmer, more saline North Atlantic inflow during the most recent period.
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A number of recent studies have shown enhanced retreat of tidewater glaciers over much of southern and western Greenland. One of the fastest retreats has occurred at Jakobshavn Isbrae, with the rapid retreat linked to the arrival of relatively warm and saline Irminger water along the west coast of Greenland. Similar links to changes in ocean water masses on the coastal shelf of Greenland were also seen on the east coast. This study presents hydrographic data from Disko Bay, additionally revealing that there was also a significant warming of the cold polar water entering Disko Bay from the mid-to-late 1990s onward. This layer, which lies at a depth of similar to 30-200 m, warmed by 1 degrees-2 degrees C. The heat content of the polar water layer increased by a factor of 3.6 for the post-1997 period compared to the period prior to 1990. The heat content in the west Greenland Irminger water layer between the same periods increased only by a factor of 2, but contained more total heat. The authors suggest that the changes in the polar water layer are related to circulation changes in Baffin Bay.
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Mass loss from the Greenland ice sheet quadrupled over the past two decades, contributing a quarter of the observed global sea-level rise. Increased submarine melting is thought to have triggered the retreat of Greenland's outlet glaciers, which is partly responsible for the ice loss. However, the chain of events and physical processes remain elusive. Recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes, multidecadal natural ocean variability and a long-term increase in the North Atlantic's upper ocean heat content since the 1950s all contributed to a warming of the subpolar North Atlantic. This led, in conjunction with increased runoff, to enhanced submarine glacier melting. Future climate projections raise the potential for continued increases in warming and ice-mass loss, with implications for sea level and climate.
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Data from a long time series of temperature, salinity, and nutrient measurements in Disko Bay (West Greenland) reveal a marked change in the water characteristics during recent years. Seasonal dynamics in the upper 150 m of the water column were highly affected by the seasonality in meteorological conditions, while the deeper water strata were more stable and were primarily influenced by large-scale circulation patterns. There was a marked increase in the average water temperatures at 200-m depth in spring 1997, with the long-term average increasing from 1.30°C to 2.25°C. Weekly data from 1996 to 1997 show that the sudden change in bottom water occurred in April 1997, due to the inflow of a larger proportion of North Atlantic water, which propagated north along the coast before entering the bay. Further support for this inflow was found when tracing the relative proportion of Atlantic water in the bay, using inorganic nutrients. These changes in the oceanography of the bay will not only lead to further glacial retreat but will also affect the local marine ecosystem by changing the relative dominance of major copepod species that overwinter in bottom waters of the bay.
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Davis Strait volume [-2.3 ± 0.7 Sv (1 Sv = 106 m3 s-1); negative sign indicates southward transport], freshwater (-116 ± 41 mSv), and heat (20 ± 9 TW) fluxes estimated from objectively mapped -004-05 moored array data do not differ significantly from values based on a 1987-90 array but are distributed differently across the strait. The 2004-05 array provided the first year-long measurements in the upper 100 mand over the shelves. The upper 100 m accounts for 39% (-0.9 Sv) of the net volume and 59% (-69 mSv) of the net freshwater fluxes. Shelf contributions are small: 0.4 Sv (volume), 15 mSv (freshwater), and 3 TW (heat) from the West Greenland shelf and -0.1 Sv, -7 mSv, and 1 TW from the Baffin Island shelf. Contemporaneous measurements of the Baffin Bay inflows and outflows indicate that volume and freshwater budgets balance to within 26% and 4%, respectively, of the net Davis Strait outflow. Davis Strait volume and freshwater fluxes nearly equal those from Fram Strait, indicating that both are significant Arctic freshwater pathways.
Article
The East Greenland Current is the main conduit for the waters of the Arctic Ocean and the Nordic Seas to the North Atlantic. In addition to low salinity Polar Surface Water and sea ice, the East Greenland Current transports deep and intermediate waters exiting the Arctic Ocean and Atlantic Water re-circulating in the Fram Strait, These water masses are already in the Fram Strait and are dense enough to contribute to the Denmark Strait overflow and to the North Atlantic Deep Water. On its route along the Greenland slope the East Greenland Current exchanges waters with the Greenland and Iceland Seas and incorporates additional intermediate water masses. In 1998 RV "Polarstern" and RV "Valdivia" occupied hydrographic sections on the Greenland continental slope from the Fram Strait to south of the Denmark Strait, crossing the East Greenland Current at nine different locations. The Arctic Ocean waters and the re-circulating Atlantic Water could be followed to just north of Denmark Strait, where the East Greenland Current encounters the northward-flowing branch of the Irminger Current. There strong mixing occurs both within the East Greenland Current and between the waters of the two currents. No distinct contribution from the Iceland Sea was observed in the Denmark Strait but the temperature reduction of the warm core of the East Greenland Current just north of the strait could partly have been caused by mixing with the colder Iceland Sea Arctic Intermediate Water. The overflow plume south of the sill was stratified and covered by a low salinity lid. Less saline overflow water was also observed on the upper part of the slope. The less saline part of the overflow was identified as Polar Intermediate Water and its properties were similar to those of the thermocline present in the East Greenland Current already in the Fram Strait. It is thus conceivable that its source is the upper (Theta < 0) part of the Arctic Ocean thermocline.
Article
In this study 36 hydrographic transects occupied between 1991 and 2007 in the vicinity of the WOCE A1E/AR7E section are used to investigate various aspects of the Irminger Gyre, a narrow cyclonic recirculation in the southwest Irminger Sea. Vertical sections of absolute geostrophic velocity were constructed using satellite and shipboard velocity measurements, and analyzed in conjunction with the hydrographic data and meteorological fields. The Irminger Gyre is a weakly baroclinic feature with a mean transport of 6.8±1.9Sv (1Sv=106m3/s). At mid-depth it contains water with the same properties as Labrador Sea Water (LSW). During the 17-year study period large changes occurred in the gyre and also within the boundary flow encircling the Irminger Sea. The gyre intensified and became more stratified, while the upper-layer circulation of the boundary current system weakened. The latter is consistent with the overall decline of the North Atlantic subpolar gyre reported earlier. However, the decline of the upper-ocean boundary currents was accompanied by an intensification of the circulation at deeper levels. The deep component of both the northward-flowing boundary current (the Irminger Current) and the southward-flowing boundary current (the Deep Western Boundary Current) strengthened. The increase in transport of the deep Irminger Current is due to the emergence of a second deep limb of the current, presumably due to a shift in pathways of the branches of the subpolar gyre. Using a volumetric water mass analysis it is argued that LSW was formed locally within the Irminger Gyre via deep convection in the early 1990s. In contrast, LSW appeared outside of the gyre in the eastern part of the Irminger Sea with a time lag of 2–3 years, consistent with transit from the Labrador Sea. Thus, our analysis clarifies the relative contributions of locally-versus remotely-formed LSW in the Irminger Sea.
Article
In August 1997, RRS Discovery cruise 230 (World Ocean Circulation Experiment (WOCE) section A25) ran a hydrographic section into Cape Farewell on the southern tip of Greenland. The closest approach to the shore was 2 nm in a water depth of 160 m over the east Greenland shelf. Analysis of the hydrographic data (conductivity-temperature-depth (CTD), vessel-mounted acoustic Doppler current profiler, and thermosalinograph) has revealed a current flowing southwestward, ∼15 km wide, 100 m deep, and centered ∼10 km offshore. We believe it to be driven by meltwater runoff from Greenland. This feature, which we call the East Greenland Coastal Current (EGCC), carries a little less than 1 Sv (106 m3 s−1) with peak current speeds of ∼1 m s−1 at the surface. The center of the EGCC lies on a salinity front with maximum salinity contrast ∼4 practical salinity units (psu) between coast and shelf break and between surface and bottom. A spot value of freshwater transport is 0.06 Sv (1800 km3 yr−1), which is equivalent to ∼30% of the Arctic freshwater gain. The presence of the EGCC and its continuity up the east Greenland coast as far as Denmark Strait is confirmed in satellite sea surface temperature images and surface drifter tracks. We estimate the sensitivity of its freshwater flux to changes in melt season mean surface air temperature to be >25% per 1°C.
Article
The general circulation of the Labrador Sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in May 1997. Surface drifters indicate three distinct speed regimes: fast boundary currents, a slower crossover from Greenland to Labrador, and a slow, eddy-dominated flow in the basin interior. Mean Eulerian velocity maps show several recirculation cells located offshore of the main currents, in addition to the cyclonic circulation of the Labrador Sea. Above the northern slope of the basin, the surface drifters have two preferential paths: one between the 1000-m and 2000-m isobaths and the other close to the 3000-m isobath. The vertical shear estimated from CTD data supports the presence of two distinct currents around the basin. One current, more baroclinic, flows between the 1000-m and 2000-m isobaths. The other one, more barotropic, flows above the lower continental slope. The Irminger Sea Water carried by the boundary currents is altered as it travels around the basin. Profiling Autonomous Lagrangian Circulation Explorer (PALACE) floats that followed approximately the Irminger Sea Water in the Labrador Sea show signs of isopycnal mixing between the interior and the boundary current in summer-fall and convection across the path of the Irminger Sea Water in winter-spring.
Article
Hydrographic data of the 1990s along World Ocean Circulation Experiment sections A1E (Greenland-Ireland) and A2 (Newfoundland-France) indicate a redistribution of cold, low-saline subarctic waters and warm, saline subtropical waters in the upper layer of the northern North Atlantic within about 2 years after the North Atlantic Oscillation had turned from a period with strong westerlies until 1995 to a period with weak westerlies in 1996 and 1997. In the latter period, subarctic waters spread preferably southward along the continental slope east of Newfoundland rather than eastward with the North Atlantic Current (NAC) into the Irminger, Iceland, and West European Basins. As a consequence, the Subarctic Front and the associated NAC shifted eastward in the Newfoundland Basin, where subarctic waters accumulate, and westward in the Iceland Basin, where a large, warm, and saline anomaly was found in 1996 and 1997, indicating a contraction of the subpolar gyre. In the Irminger Basin the anomaly occurred in 1998 and 1999. Whereas the cyclonic circulation in the Irminger and Iceland Basins weakened, it intensified in the Newfoundland Basin, where a strengthened Labrador Current retroflection joined the NAC. This and the increased anticyclonic recirculation of subtropical waters in the Newfoundland and West European Basins caused a considerable reduction of the northward heat transport across 47°N in the upper layer in 1997. The anticyclonic circulation occurring in the West European Basin suggested a northward expansion of the subtropical gyre.
Article
We have developed an automatic method to identify changes in the position of calving glacier margins using daily MODIS imagery. Application of the method to 32 ocean-terminating glaciers in East Greenland produced 26,802 margin positions for a 10 year long period (2000-2009). We report these high-resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width. Despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 degrees N. All glaciers above this latitude showed very limited or no change when seasonality was excluded, while glaciers south of 69 degrees N retreated significantly between 2001 and 2005 (similar to 2.3 km on average). Approximately 26% of the retreat of southern glaciers was regained by readvance from 2005 to 2009. To explain the latitudinal boundary of glacier dynamics, we review basic climatic factors, including summer and winter atmospheric forcing, sea ice conditions, and ocean temperature. We conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the Irminger Sea and to fjords and coastal regions south of 69 degrees N. Northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 degrees N are less exposed to subtropical waters. The southern retreats illustrate sensitive behavior of calving glaciers, and we hypothesize that the calving fronts retreated because they were exposed to rapid ice-front melting.
Article
The ice sheets of Greenland and Antarctica are losing ice at accelerating rates, much of which is a response to oceanic forcing, especially of the floating ice shelves. Recent observations establish a clear correspondence between the increased delivery of oceanic heat to the ice-sheet margin and increased ice loss. In Antarctica, most of these processes are reasonably well understood but have not been rigorously quantified. In Greenland, an understanding of the processes by which warmer ocean temperatures drive the observed retreat remains elusive. Experiments designed to identify the relevant processes are confounded by the logistical difficulties of instrumenting ice-choked fjords with actively calving glaciers. For both ice sheets, multiple challenges remain before the fully coupled ice-ocean-atmosphere models needed for rigorous sea-level projection are available.
Article
Observations between 1997 and 2001, of a 30% velocity increase and up to 60 m thinning of downstream parts of Jakobshavn Isbrae, Greenland, immediately following calving of about 4 km of its 15 km floating ice tongue, suggest that acceleration may have been initiated by the calving. Assuming that the force perturbation associated with such weakening is swiftly transmitted far up-glacier, I develop equations to estimate the perturbation. Initially, the observed changes are consistent with the comparatively small perturbation associated with the calving. Thereafter, it was probably sustained by thinning of the remaining ice tongue at rates of about 80 m a−1. Otherwise, the force perturbation would soon have been balanced by reduction in the hydrostatic driving force for longitudinal creep as the glacier thinned, with velocities dropping to their former values. The calculated force perturbation increases to a maximum about 10 km inland of the grounding line, consistent with decreasing weight forces as the glacier thins over bedrock that slopes uphill seawards. Further inland, it progressively decreases, probably because marginal drag increased as the glacier accelerated. Both here and on the floating tongue, marginal ice appears to have been softened by the influence of locally intense shear on ice temperature and/or fabric. More recent observations show continued acceleration and thinning, and most of the remaining ice tongue calved away in April 2003, so thinning is likely to continue.
Article
Six historical sections across the West Greenland Current are examined. Three sections have been regularly occupied since the late 1950s, while the three southern ones have been taken since 1984. Significant variability is observed for the freshwater core of the coastal current on the shelf, with salinity varying by over 3 units between years. There is also significant variability in the shape and offshore position of the main shelf break front, leading to large variability in Eulerian velocities. Significant presence of Irminger Water is seen during the 1960s and the 2000s, being found right across the sections in recent years. Maximum mean transport relative to the 34.8 isohaline of , relative to 700 db, for 1984–2005, is observed at the Cape Desolation section. Transports decrease to the north, with the majority of the exchange with the interior of the Labrador Sea occurring between Cape Desolation and Fylla Bank. Inter-decadal transport variability is observed at Fylla Bank while a decline in transports since peaks in the early 1990s is seen at Cape Farewell and Cape Desolation. Freshwater transport is largest at Cape Desolation, with a mean Summer transport of . Freshwater transport increases slightly between Cape Farewell and Cape Desolation and we suggest it is related to local discharge by glaciers into Juliannehaab Bight, as well as the melting of sea-ice. We also find that years of high Greenland ice cap melt are consistently associated with years of high freshwater transport at Cape Desolation, suggesting a portion of the freshwater transport of the West Greenland Current may be associated with melt from the Greenland ice sheet. Finally, significantly enhanced freshwater transports (33 mSv at Cape Desolation compared to the long term mean) are seen in 2008, probably a signature of the record Arctic Ocean ice melt and export in 2007.
Article
Saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next, depending on the source of bottom water. Flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next. Examples in the Atlantic include flow in the Romanche Fracture Zone, the Vema Channel, the Ceara Abyssal Plain, the Anegada-Jung-fern passage, and the Discovery Gap, but there are many more. Theoretical predictions of volume flux using a method that requires only conductivity-temperature-depth data archives and detailed knowledge of bathym-etry near the saddle point are compared with volume flux estimates using current meters and/or geostrophic estimates for seven cases. The ratio of prediction to volume flux estimate ranges from 1.0 to 2.7. Some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins. Theory of the influence of rotation on such critical flows is reviewed. Predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods.
Article
1] We examine the historical variability of Irminger Water (IW) along 3 sections across the West Greenland Current over 1950 – 2005. Significant variability in the salinity, size and position of the IW core are seen over time. Some of the saltiest and warmest IW ever recorded have been seen since 1995 (comparable to previous maximums in the 1960s). During these periods, the volume of IW is also larger, leading to larger transports into the Labrador Sea. For the period 1984 – 2005 transports at Cape Farewell are 3.8 ± 0.9 Sv, 7.5 ± 2.2 Â 10 13 J and 8.5 ± 1.8 mSv of salt referenced to 35.0. LSW formation is also correlated to IW transport at Cape Farewell with a lag of one year (0.51).
Article
An understanding of the interaction between ice sheet dynamics and forcing mechanisms, such as oceanic and atmospheric circulation, is important because of the potential contribution of these processes to constraining models that seek to predict future rates of sea-level change. Here we report new benthic foraminiferal data from Disko Bugt, West Greenland, showing a close correlation between subsurface ocean temperature changes and the ice margin position of the glacier Jakobshavn Isbrae over the past 100 yr. In particular, our faunal data show that warm ocean currents entered a bay, Disko Bugt, during the retreat phases of Jakobshavn Isbrae from A.D. 1920 to 1950 and since 1998. We also show a link between West Greenland ocean temperature and the Atlantic Multidecadal Oscillation, a key climate indicator in the North Atlantic Ocean. The close coupling between the oceans and the cryosphere identifi ed here should be assessed in future projections of sea-level change.
Article
Volume, freshwater and heat transport through Davis Strait, the northern boundary of the Labrador Basin, are computed using a mooring array deployed for three consecutive years. The net volume, freshwater and heat transports are , , . Both southward and northward volume and freshwater transports are maximum in November. The seasonal variability is dictated by the variability in the main water mass transports: Irminger Sea Water, West Greenland shelf water, surface meltwater, and a cold intermediate layer (CIL) originating from Lancaster Sound. The southward freshwater transport seasonal amplitude is dominated by the CIL transport rather than the surface meltwater layer. Sea-ice transport through Davis Strait deduced from remote sensing data is equal to which is much smaller than equivalent estimates for Fram Strait. Using these new estimates, we attempt to close the Arctic Ocean volume and freshwater budget.
Article
The oceanographic, meteorological and sea-ice conditions in Baffin Bay are studied using historical hydrographic, satellite and meteorological data, and a set of current meter data from a mooring program of the Bedford Institute of Oceanography. Baffin Bay is partially covered by sea-ice all year except August and September. The interannual variation of the ice extent is shown to be correlated with winter air temperature. Available hydrographic data were used to study the water masses and the horizontal and vertical distribution of temperature/salinity. Three water masses can be identified – Arctic Water in the upper 100–300 m of all regions except the southeast, West Greenland Intermediate Water at 300–800 m in most of the interior of Baffin Bay, and Deep Baffin Bay Water in all regions below 1200 m. The temperature and salinity in Baffin Bay have limited seasonal variability except in the upper 300 m of eastern Davis Strait, northern Baffin Bay and the mouth of Lancaster Sound. Summer data have a temperature minimum at ∼100 m, which suggests winter convection does not penetrate deeper than this depth. Current meter data and results of a circulation model indicate that the mean circulation is cyclonic. The seasonal variation of the currents is complex. Overall, summer and fall tend to have stronger currents than winter and spring at all depths. Among the different regions, the largest seasonal variation occurs at the mouth of Lancaster Sound and the Baffin Island slope. Model generated velocity fields show a basic agreement with the observed currents, and indicate strong topographic control in the vicinity of Davis Strait and on the Greenland shelves. The model also produces a southward counter current on the Greenland slope, which may explain the observed high horizontal shears over the Greenland slope. Estimates of the volume and fresh water transports through Lancaster, Jones and Smith Sounds are reviewed. Transports through Davis Strait are computed from the current meter data. The balance of freshwater budget and sensitivity of the thermohaline circulation to freshwater transport are discussed.
Article
Jakobshavn Isbræ is the most active glacier in Greenland, with an annual discharge of about 30 km3 of ice, and it is one of the few recently surveyed glaciers to thicken between 1993 and 1998, despite locally warm summers. Repeated airborne laser-altimeter surveys along a 120 km profile in the glacier basin show slow, sporadic thickening between 1991 and 1997, suggesting a small positive mass balance, but since 1997 there has been sustained thinning of several ma 1 within 20 km of the ice front, with lower rates of thinning further inland. Here, we use weather-station data from the coast and the ice sheet to estimate the effects on surface elevation of interannual variability in snowfall and surface melt rates, and thus to infer the temporal and spatial patterns of dynamic thinning. These show the glacier to have been close to balance before 1997 followed by a sudden transition to rapid thinning, initially confined to the lower reaches of the glacier (below about 500 m elevation), but progressively spreading inland until, between 1999 and 2001, thinning predominated over the entire surveyed region, up to 2000 m elevation. If this continues, the glacier calving from and probably its grounding line will retreat substantially in the very near future.
Article
The subtidal circulation of the southeast Greenland shelf is described using a set of high-resolution hydrographic and velocity transects occupied in summer 2004. The main feature is the East Greenland Coastal Current (EGCC), a low-salinity, high-velocity jet with a wedge-shaped hydrographic structure characteristic of other surface buoyancy-driven currents. The EGCC was observed along the entire Greenland shelf south of Denmark Strait, while the transect north of the strait showed only a weak shelf flow. This observation, in conjunction with water mass considerations and other supporting evidence, suggests that the EGCC is an inner branch of the East Greenland Current (EGC) that forms south of Denmark Strait. It is argued that bathymetric steering is the most likely reason why the EGC apparently bifurcates at this location. Repeat sections occupied at Cape Farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the EGCC and EGC on timescales of 2-3 days. Accounting for the wind-induced effects, the volume transport of the combined EGCC/EGC system is roughly constant (∼2 Sv) over the study domain, from 68°N to Cape Farewell near 60°N. The corresponding freshwater transport increases by roughly 60% over this distance (59-96 mSv, referenced to a salinity of 34.8). This trend is consistent with a simple freshwater budget of the EGCC/EGC system that accounts for meltwater runoff, melting sea-ice and icebergs, and net precipitation minus evaporation.
Article
Observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid- to high-latitude North Atlantic Ocean. TOPEX/Poseidon altimeter data show that subpolar sea surface height increased during the 1990s, and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation. Combining the data from earlier satellites, we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s. Direct current-meter observations in the boundary current of the Labrador Sea support the weakening circulation trend of the 1990s and, together with hydrographic data, show that the mid- to late 1990s decline extends deep in the water column. Analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations: A weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation.
Article
It is important to understand recent changes in the velocity of Greenland glaciers because the mass balance of the Greenland Ice Sheet is partly determined by the flow rates of these outlets. Jakobshavn Isbrae is Greenland's largest outlet glacier, draining about 6.5 per cent of the ice-sheet area, and it has been surveyed repeatedly since 1991 (ref. 2). Here we use remote sensing data to measure the velocity of Jakobshavn Isbrae between 1992 and 2003. We detect large variability of the velocity over time, including a slowing down from 6,700 m yr(-1) in 1985 to 5,700 m yr(-1) in 1992, and a subsequent speeding up to 9,400 m yr(-1) by 2000 and 12,600 m yr(-1) in 2003. These changes are consistent with earlier evidence for thickening of the glacier in the early 1990s and rapid thinning thereafter. Our observations indicate that fast-flowing glaciers can significantly alter ice discharge at sub-decadal timescales, with at least a potential to respond rapidly to a changing climate.
Article
During the past decade, record-high salinities have been observed in the Atlantic Inflow to the Nordic Seas and the Arctic Ocean, which feeds the North Atlantic thermohaline circulation (THC). This may counteract the observed long-term increase in freshwater supply to the area and tend to stabilize the North Atlantic THC. Here we show that the salinity of the Atlantic Inflow is tightly linked to the dynamics of the North Atlantic subpolar gyre circulation. Therefore, when assessing the future of the North Atlantic THC, it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account.
The International Thermodynamic Equation of Seawater—2010: Calculation and use of thermodynamic properties
IOC, SCOR, and IAPSO, 2010: The International Thermodynamic Equation of Seawater—2010: Calculation and use of thermodynamic properties. Intergovernmental Oceanographic Commission, Manuals and Guides 56, 220 pp. [Available online at http://www.teos-10.org/pubs/TEOS-10_Manual.pdf.]
Oceanographic investigations off west Greenland 2012. NAFO Scientific Council Documents Tech. Rep. 13/003, 50 pp. [Available online at http://ocean.dmi.dk/staff
——, 2013: Oceanographic investigations off west Greenland 2012. NAFO Scientific Council Documents Tech. Rep. 13/003, 50 pp. [Available online at http://ocean.dmi.dk/staff/mhri/Docs/ scr13-003.pdf.]