Trond Dokken

• PhD
• Research Director at Uni Research

Species assemblage composition of marine microfossils offers the possibility to investigate ecological and climatological change on time scales inaccessible using conventional observations. Planktonic foraminifera - calcareous zooplankton - have an excellent fossil record and are used extensively in palaeoecology and palaeoceanography. During the L...

Constraining the past sea ice variability in the Nordic Seas is critical for a comprehensive understanding of the abrupt Dansgaard- Oeschger (D-O) climate changes during the last glacial. Here we present unprecedentedly detailed sea ice proxy evidence from two Norwegian Sea sediment cores and an East Greenland ice core to resolve and constrain sea...

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrai...

Abrupt climate change is a striking feature of many climate records, particularly the warming events in Greenland ice cores. These abrupt and high-amplitude events were tightly coupled to rapid sea-ice retreat in the North Atlantic and Nordic Seas, and observational evidence shows they had global repercussions. In the present-day Arctic, sea-ice lo...

Rapid warmings epitomize the Dansgaard-Oeschger events that are recorded in Greenland ice cores and imprinted in ocean sediment cores. While the abrupt climate changes appear connected to perturbations in sea ice and ocean circulation, it is unclear how the water masses within the Nordic Seas responded and were influenced by the inflowing Atlantic...

Rapid changes in ocean circulation and climate have been observed in marine-sediment and ice cores over the last glacial period and deglaciation, highlighting the non-linear character of the climate system and underlining the possibility of rapid climate shifts in response to anthropogenic greenhouse gas forcing. To date, these rapid changes in cli...

Constraining the response time of the climate system to changes in North Atlantic Deep Water (NADW) formation is fundamental to improving climate and Atlantic Meridional Overturning Circulation predictability. Here we report a new synchronization of terrestrial, marine, and ice-core records, which allows the first quantitative determination of the...

The last glacial period was marked by pronounced millennial-scale variability in ocean circulation and global climate. Shifts in sea ice cover within the Nordic Seas are believed to have amplified the glacial climate variability in northern high latitudes and contributed to abrupt, high-amplitude temperature changes over Greenland. We present unpre...

Dansgaard-Oeschger (D-O) climate instabilities that took place during Marine Isotope Stage 3 are connected to changes in ocean circulation patterns and sea ice cover. Here we explore in detail the configuration of the water column of the Denmark Strait during D-O events 8–5. How the ocean currents and water masses within the Denmark Strait region r...

Thanks to its optimal location on the northern Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e., Greenland stadials). These...

Thanks to its optimal location on the North Brazilian margin, core MD09-3257 records both ocean circulation and atmospheric changes. The latter occur locally in the form of increased rainfall on the adjacent continent during the cold intervals recorded in Greenland ice and northern North Atlantic sediment cores (i.e. Greenland stadials). These rain...

Sediment cores from the south-eastern Nordic Seas simultaneously archive the variability of the Fennoscandian Ice Sheet (FIS), the British-Irish Ice Sheet (BIIS) and the regional oceanic conditions. This study aims to con- tribute to our understanding of the marine-based section of the FIS and the BIIS between 35,000 and 15,000 years BP, by using c...

The region offshore North Iceland is known to be sensitive to broad scale climatic and oceanographic changes in the North Atlantic Ocean. Changes in surface and subsurface water conditions link to the varying influence of Polar-sourced East Icelandic Current (EIC) and Atlantic-sourced North Irminger Icelandic Current (NIIC). Cold/fresh Polar waters...

The extent of the NW European ice sheet during the Last Glacial Maximum is fairly well constrained to, at least in periods, the shelf edge. However, the exact timing and varying activity of the largest ice stream, the Norwegian Channel Ice Stream (NCIS), remains uncertain. We here present three sediment records, recovered proximal and distal to the...

It has been proposed that the rapid rise of atmospheric CO2 across the last deglaciation was driven by the release of carbon from an extremely radiocarbon-depleted abyssal ocean reservoir that was ‘vented’ to the atmosphere primarily via the deep- and intermediate overturning loops in the Southern Ocean. While some radiocarbon observations from the...

During the last glacial period, Greenland's climate shifted between cold (stadial) and warm (interstadial) phases that were accompanied by ocean circulation changes characterized by reduced Atlantic Meridional Overturning Circulation (AMOC) during stadials. Here, we present new data from the western tropical Atlantic demonstrating that AMOC slowdow...

The understanding of climate and climate change is fundamentally concerned with two things: a well-defined and sufficiently complete climate record to be explained, for example of observed temperature, and a relevant mechanistic framework for making closed and consistent inferences concerning cause-and-effect. This is the case for understanding obs...

he separate roles of oceanic heat advection and orbital forcing on influencing early Holocene temperature variability in the eastern Nordic Seas is investigated. The effect of changing orbital forcing on the ocean temperatures is tested using the 1DICE model, and the 1DICE results are compared with new and previously published temperature reconstru...

[1] Dansgaard-Oeschger (D-O) cycles are the most dramatic, frequent, and wide-reaching abrupt climate changes in the geologic record. On Greenland, D-O cycles are characterized by an abrupt warming of 10 ± 5°C from a cold stadial to a warm interstadial phase, followed by gradual cooling before a rapid return to stadial conditions. The mechanisms re...

Benthic foraminiferal Mg/Ca has been shown to have great potential as a proxy for reconstructing deep water temperatures. However, the exact relationship between Mg uptake in benthic foraminifera and temperature is still ambiguous, and further exploration and refinement is much needed to reduce uncertainties associated with the method. Here, we pre...

Dansgaard-Oeschger (D-O) cycles are the most dramatic, frequent, and wide-reaching abrupt climate changes in the geologic record. On Greenland, D-O cycles are characterized by an abrupt warming of 10 ± 5°C from a cold stadial to a warm interstadial phase, followed by gradual cooling before a rapid return to stadial conditions. The mechanisms respon...

The Atlantic Meridional Overturning Circulation (AMOC), through the North Brazil Current (NBC), has a significant role for the budget of heat and salt of the North Atlantic and changes on its strength are known to have profound impacts on global climate. Studies based on modeling suggested that, from annual to multi-decadal time scales, a slowdown...

Heinrich events, identified as enhanced ice-rafted detritus (IRD) in North Atlantic deep sea sediments (Heinrich, 1988; Hemming, 2004) have classically been attributed to Laurentide ice-sheet (LIS) instabilities (MacAyeal, 1993; Calov et al., 2002; Hulbe et al., 2004) and assumed to lead to important disruptions of the Atlantic meridional overturni...

The separate roles of oceanic heat advection and orbital forcing on influencing early Holocene temperature variability in the eastern Nordic Seas is investigated. The effect of changing orbital forcing on the ocean temperatures is tested using the 1DICE model, and the 1DICE results are compared with new and previously published temperature reconstr...

Heinrich events, identified as enhanced ice-rafted detritus (IRD) in North Atlantic deep sea sediments (Heinrich, 1988; Hemming, 2004) have classically been attributed to Laurentide ice-sheet (LIS) instabilities (MacAyeal, 1993; Calov et al., 2002; Hulbe et al., 2004) and assumed to lead to important disruptions of the Atlantic meridional overturni...

The distribution of rainfall in tropical Africa is controlled by the African rainbelt(1), which oscillates on a seasonal basis. The rainbelt has varied on centennial to millennial timescales along with changes in Northern Hemisphere high-latitude climate(2-5), the Atlantic meridional overturning circulation(6) and low-latitude insolation(7) over th...

The distribution of rainfall in tropical Africa is controlled by the African rainbelt**1, which oscillates on a seasonal basis. The rainbelt has varied on centennial to millennial timescales along with changes in Northern Hemisphere high-latitude climate**2, 3, 4, 5, the Atlantic meridional overturning circulation**6 and low-latitude insolation**7...

Marine isotope stage 3 (29–59 kyr BP) is characterised by rapid shifts from cold stadial to warm interstadial periods, which may be linked to changes in the vigour of the Atlantic Meridional Overturning Circulation due to variable freshwater input by melting ice. Here we present two northern North Atlantic multi-proxy records of sea surface conditi...

Marineisotopestage3(29e59 kyrBP)ischaracterisedbyrapidshiftsfromcoldstadialtowarminterstadial periods,whichmaybelinkedtochangesinthevigouroftheAtlanticMeridionalOverturningCirculation due tovariablefreshwaterinputbymeltingice.HerewepresenttwonorthernNorthAtlanticmulti-proxy recordsofseasurfaceconditionsthatindicatewarm(near)seasurfaceconditionsduri...

Heinrich event 1 triggered through warmer Nordic subsurface waters

Multi-proxy data representative for the surface and subsurface layer has been compiled for three sites from the eastern Nordic Seas. The surface proxy is alkenone based SST's, while foraminiferal abundance data, Maximum Likelihood foraminiferal based SST estimates, and oxygen isotope measurements on planktic foraminifera were used to reconstruct su...

The tropical rainbelt delivers nearly all of the rainfall between 20°N and 20°S in Africa and so is a vital part of the African climate system. On millennial timescales, rainfall fluctuations in Africa are commonly attributed to a latitudinal migration in the position of the rainbelt. However, this mechanism is not consistent with new proxy data, w...

A cruise with the research vessel G.O. SARS was carried out from 07 to 20 December 2007 within the framework of the European Science Foundation (EuroMARC) project RETRO, which aims to reconstruct changes within the thermocline in the tropics during periods of reduced Meridional Overturning Circulation (MOC). As part of this strategy we need a best...

The last deglaciation (21 ka B.P. to ≃ 7 ka B.P.) is the most recent major climate transition that occured on Earth. During this period, changes in insolation and atmospheric greenhouse gases melted the major northern hemisphere ice-sheet leaving only Greenland as we know it today. The last deglaciation presents a unique opportunity in the climat...

The large semi-arid regions of Africa bordering the equatorial regions are prone to drought. It is thus important to understand the mechanisms influencing African rainfall. Most of the rain in Africa is delivered by the tropical rainbelt, which oscillates seasonally between 20°N and 20°S. The distribution of rainfall is determined by the latitude,...

The Holocene is commonly referred to as a period of relatively stable climate conditions. It is however affected by a climate anomaly 8.2 kyr ago, postulated to be the result of weakened Meridional Overturning Circulation (MOC) triggered by a freshwater outburst. This time period offers then a good opportunity to study the relationship between inte...

The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation1, 2, 3. Environmental changes during this period have been documented by both proxy-based reconstructions3 and model simulations4, but...

The Younger Dryas event, which began approximately 12,900 years ago, was a period of rapid cooling in the Northern Hemisphere, driven by large-scale reorganizations of patterns of atmospheric and oceanic circulation(1-3). Environmental changes during this period have been documented by both proxy-based reconstructions(3) and model simulations(4), b...

Observation-based reconstructions of sea surface temperature from relatively stable periods in the past, such as the Last Glacial Maximum, represent an important means of constraining climate sensitivity and evaluating model simulations. The first quantitative global reconstruction of sea surface temperatures during the Last Glacial Maximum was dev...

This article was submitted without an abstract, please refer to the full-text PDF file.

This article was submitted without an abstract, please refer to the full-text PDF file.

Dansgaard-Oeschger (D-O) events are abrupt warming events occurring intermittently throughout much of the last glacial period, but most prominently during marine isotope stage 3 (MIS3, 60-30Ka). Marine and ice core data suggest that North Atlantic climate shifted between cold stadial and warm interstadial states within decades, involving large chan...

The Younger Dryas (YD) was a period of rapid cooling resulting from large-scale reorganizations of the atmospheric and oceanic circulation patterns at the end of the last glaciation. Environmental changes associated with the YD have been inferred from a large variety of proxy records in both hemispheres, as well as by model simulations. However, a...

Twenty benthic oxygen isotope records from different water depths in the Nordic seas and the North Atlantic are compared. During the Last Glacial Maximum, brine formation on continental shelves produced Brine Shelf Water (BSW), sinking below 1500 m in the Nordic seas. Open-ocean convection in the Nordic seas produced Glacial North Atlantic Intermed...

The Last Glacial Maximum climate is one of the classical benchmarks used both to test the ability of coupled models to simulate climates different from that of the present-day and to better understand the possible range of mechanisms that could be involved in future climate change. It also bears the advantage of being one of the most well documente...

The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the...

About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined...

Faroe-Shetland Channel (FSC) is the principal conduit for both outflow of Norwegian Sea water to the N.E. Atlantic and inflow of N. Atlantic surface water to the Norwegian Sea. Gravity core HM03-133-25 comes from the southern end of FSC in a pond of relatively thick Holocene accumulation. The site is swept by strong currents, yielding high sand con...

Faroe-Shetland Channel (FSC) is the principal conduit for both outflow of Norwegian Sea water to the N.E. Atlantic and inflow of N. Atlantic surface water to the Norwegian Sea. Gravity core HM03-133-25 comes from the southern end of FSC in a pond of relatively thick Holocene accumulation. The site is swept by strong currents, yielding high sand con...

Within the frame of the multiproxy approach for the reconstruction of the glacial ocean (MARGO) project, sea-surface conditions of the Last Glacial Maximum (LGM, 23–19 ka) were reconstructed using different proxies, which were calibrated to a standardized modern hydrography. In the North Atlantic, the revised LGM MARGO data set provides a comprehen...

In core top samples in the Nordic Seas, Mg/Ca ratios of N. pachyderma (sin.) are generally consistent with previous high-latitude calibration data but do not reflect the modern calcification temperature gradient from 2°C in the northwest to 8°C in the southeast. This is because Mg/Ca ratios in foraminiferal shells from the central Nordic Seas are ~...

The penultimate termination has been studied with focus on oceanographic changes in the eastern Nordic Seas and the influence of these changes on the surrounding ice sheets and vice versa. Repeatedly, major changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) occurred during the studied interval. Times of strong overtur...

We review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the MARGO project for the Late Holocene time slice. The data set consists of over 2100 data from recent sediment with thorough age con...

The aim of this overview paper is to provide a brief synthesis of the five review papers contained in the monograph. Prevailing south-westerly winds, oceanic flow patterns, and oceanic summer heat storage make the Nordic Seas region having temperatures 10 to 20 °C above the mean temperature at similar latitudes. The combination of the large heat im...

Climate change is one of the most pressing issues facing the world today. With increasing levels of greenhouse gases in the atmosphere, climate changes will play an increasing role for society in the future. The Bjerknes Centre for Climate Research (BCCR) is a joint climate research venture between the University of Bergen (UoB), the Institute of M...

The world's largest positive temperature deviation from zonal mean temperatures lies within the realm of the Nordic Seas, comprising bodies of water variously referred to as the Norwegian Sea, the Iceland Sea, and the Greenland Sea. Its role as a mixing cauldron for waters entering from the North Atlantic and the Arctic Oceans, and its function as...

This paper presents an exploratory synthesis of quantitative temperature reconstructions during the last deglaciation in Norway and the Norwegian Sea. The variety of proxy data available permits an overview of climate development and comparisons between land and sea records. Temperature reconstructions from each available proxy were averaged for th...

Variable climatic and oceanographic conditions characterized the last inter-glacial at high northern latitudes, probably related to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC). The magnitudes of these changes are comparable to the Holocene variability, and were thus significantly subdued compared to glacial cli...

We review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the MARGO project for the Late Holocene time slice. The data set consists of over 2100 data from recent sediment with thorough age con...

During the last glacial period, climatic variation in the Northern and Southern Hemispheres was evidently linked. Modelling work points to freshwater discharge into the North Atlantic as a driving factor.

Many paleoceanographic reconstructions of the glacial North Atlantic include estimates of iceberg discharge, which are based on the variable abundance of ice-rafted detritus (IRD) in deep-sea sediments. IRD abundance is most often determined by the mechanical separation and painstaking counting of terrigenous particles larger than a specified thres...

Precise documentation of past variations in the strength of thermohaline circulation (THC) is critical for the understanding of the mechanisms and dynamics of changes in climate and carbon cycle. Here we present a record of changes in the strength of the North Atlantic bottom current obtained from a mineral magnetic study of high accumulation rate...

Large temperature variations on land, in the air, and at the ocean surface, and highly variable flux of ice‐rafted debris (IRD) delivered to the North Atlantic Ocean show that rapid climate fluctuations took place during the last glacial period. These quasi‐periodic, high‐amplitude climate variations followed a sequence of events recognized as a ra...

We here present proxy data on decadal scale resolution from marine climate records from the North-Atlantic/Nordic Seas, collected during IMAGES cruises with R/V Marion Dufresne in 1995 and 1999. These records are compared with SST records from western tropical Atlantic and ice core records from Greenland and Antarctica. This study is about the last...

Marine Isotope Stage 5 (MIS 5) has been studied at high resolution in three cores from the Nordic Seas. Cores MD99-2303 (77^o31.18N, 08^o23.98E: 2277 m depth) and MD99-2304 (77^o37.26N, 09^o56.90E: 1315 m depth) are located at the West Spitsbergen margin, while MD95-2010 (66^o41.05N, 04^o33.97E: 1226 m depth) is from the Vøring Plateau. The cores a...

Ice core data and marine records suggest an inter-hemispheric out of phase relationship during D/O events during the last glacial period, and during the last deglaciation. Here we present multi-proxy results from sediment cores from the Nordic Seas and the North Atlantic that can be directly compared with ice core records and Sea Surface Temperatur...

The Vedde Ash Bed has been identified in several marine sediment cores and represents an important time-marker for the mid/upper Younger Dryas cooling. The age of the Vedde Ash Bed is dated to 10,310 radiocarbon years and 11,980 ice core years. In the present paper we present Vedde Ash time slice maps based on published and unpublished data from 40...

IMAGES V cores MD99-2303 (77°31.18N, 08°23.98W: 2277m water depth) and MD99-2304 ((77°37.26N, 09°56.90W: 1315m water depth) provide high resolution information about high latitude climate variability during Termination II and MIS 5. Here we report a study of stable isotopes, ice rafted debris and magnetic properties in these cores with a detailed f...

We have synchronized records of ice-rafted rock debris deposits of three sediment cores from the Norwegian Sea and the Irminger Basin during the last glacial period from 10 to 50 ka by combining the use of radiocarbon dates and adjustments of physical properties. Our synchronized records indicate that layers rich in ice-rafted debris were deposited...

We have investigated five sediment cores from the margin and abyssal plain off western Svalbard-Barents Sea in the polar North Atlantic. We discuss the palaeoceanography and its relationship to glacial history during the last interglacial–glacial cycle based on detailed stratigraphic analyses of planktic and benthic foraminiferal fauna, oxygen and...

High-amplitude, rapid climate fluctuations are common features of glacial times. The prominent changes in air temperature recorded in the Greenland ice cores(1,2) are coherent with shifts in the magnitude of the northward heat flux carried by the North Atlantic surface ocean(3,4); changes in the ocean's thermohaline circulation are a key component...

The bulk magnetic parameters of seven deep-sea cores distributed from the Nordic Seas (67°N) to the North Atlantic as far south as the Bermuda Rise (33°N) exhibit short-term variations which correlate with rapid climatic changes during marine isotopic stage 3 (MIS3). The magnetic mineralogy is uniformly dominated by well sorted low Ti-content mag...

Taking advantage of the continuous high resolution magnetic techniques, we have studied the magnetic properties of six deep-sea cores located in the Nordic seas and in North Atlantic along an E-W transect between 58° to 67°N. The study has been focussed on climatic stage 3 during which these cores exhibit large amplitude short term variations in th...