Kristinn Gudmundsson

Kristinn Gudmundsson
Marine and Freshwater Research Institute | MRI · Pelagic and environmental section

Cand. real

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27
Publications
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348
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Featured research
Article
Full-text available
This study compares inter-annual dynamics of the two biomass dominant copepods in the Iceland Sea, the North Atlantic species Calanus finmarchicus and the Arctic C. hyperboreus, in an era of relatively low temperatures in the beginning of the study period (1990-1995) and higher temperatures thereafter. Samples were collected annually in May along a cross-shore transect of eight stations. The long-term variability in abundance of the two Calanus species was analysed in relation to hydrography, nutrients and phytoplankton dynamics, and large-scale climatic changes in the North Atlantic Ocean. Sea surface temperatures showed an increasing trend from the beginning to the end of the time series for all stations. From the end of the 1990s, C. finmarchicusshowed an increasing trend at the outermost station, whereas C. hyperboreus generally showed a decreasing trend along the whole transect from the mid-2000s. For both species, temperature was the single most important environmental factor explaining variance in abundance, however with opposite effects for the Arctic (C. hyperboreus) and the Atlantic (C. finmarchicus) species. It is hypothesized that warming north of Iceland may lead to increase of C. finmarchicus abundance through increased recruitment and advection, and decreased C. hyperboreus abundance. The change in species composition may in turn influence upper trophic levels, e.g. the capelin, the region’s main planktivorous fish.
Article
Full-text available
Since the article “Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades” by Kulk et al. [1] was published, we discovered an error in the code of the primary production model, which crept in when the code was updated from the original version described by Platt and Sathyendranath (1988), Sathyendranath et al. (1995) and Longhurst et al. (1995) ([2,31,52] in [1]). The main error in the code led to a time interval for the integration of daily water-column primary production that was shorter than it should have been. As a consequence, daily surface irradiance and hence primary production were systematically underestimated by 20–25% for the entire time series. We also discovered that the Photosynthetic Active Radiation (PAR) products of the National Aeronautics and Space Administration (NASA) that were used to scale the daily light cycle were rounded down for 2003–2019 (MODIS years), which led to an additional but small underestimation of daily surface irradiance. In addition to addressing these errors, we have included a merged time series of the PAR product to remove inter-sensor biases (as described in the corrected text of Appendix B; see below). The main corrections increased our estimate of global annual primary production on average by +23.9% between 1998 and 2018, while the correction of the rounding error in the PAR products increased global annual primary production between 2003 and 2018 by +0.9%. Inclusion of the merged PAR product in the primary production model caused a −0.25% decrease in global annual primary production between 1998 and 2002 and a +0.08% increase between 2003 and 2010 (relative to the aforementioned +23.9% increase for the entire time series). Our estimate of global annual primary production between 1998 and 2018 now is 48.7 to 52.5 Gt C y−1 instead of the published estimate of 38.8 to 42.1 Gt C y−1. Although this is a substantial increase in the estimate of primary production, the results of the sensitivity analysis in which the photosynthesis versus irradiance parameters were varied by ±1 standard deviation and, importantly, the observed trends in regional and global annual primary production are largely unchanged. We therefore consider the outcomes of the study still valid after the corrections. We also note that our corrected estimate of global annual primary production is still within the range of earlier reports (32.0–70.7 Gt C y−1 [5,104] in [1]). The corrected paragraphs, tables and figures appear below. All references mentioned below can be found in the original article [1]. The corrections affect a number of results, but the nature of the corrections is largely the same: the magnitude of primary production has increased significantly everywhere, whereas the trends have been affected only marginally, and the major conclusions remain unchanged, except for the magnitude of marine primary production. The authors apologise for any inconvenience caused. The original article has been updated.
Technical Report
Full-text available
Abstract A sampling dedicated for the project “Ecologically and economically sustainable mesopelagic fisheries” (MEESO), funded by the European Union, took place during a cruise designed to study pelagic ecosystems of the Nordic Seas during summer (IESSNS) in July 2020. The main aim of the MEESO work was to study the abundance, distribution and composition of mesopelagic organisms in relation to hydrography and phytoplankton productivity. The focus was on a longitudinal transect along ~61°50’N, from ~38°49’W to ~16°05’W, from the Irminger Sea and into the Iceland Basin and including a station in Grindavík basin.
Article
Full-text available
Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. One of the major challenges in this approach lies in the assignment of the appropriate model parameters that define the photosynthetic response of phytoplankton to the light field. In the present study, a global database of in situ measurements of photosynthesis versus irradiance (P-I) parameters and a 20-year record of climate quality satellite observations were used to assess global primary production and its variability with seasons and locations as well as between years. In addition, the sensitivity of the computed primary production to potential changes in the photosynthetic response of phytoplankton cells under changing environmental conditions was investigated. Global annual primary production varied from 38.8 to 42.1 Gt C yr - 1 over the period of 1998–2018. Inter-annual changes in global primary production did not follow a linear trend, and regional differences in the magnitude and direction of change in primary production were observed. Trends in primary production followed directly from changes in chlorophyll-a and were related to changes in the physico-chemical conditions of the water column due to inter-annual and multidecadal climate oscillations. Moreover, the sensitivity analysis in which P-I parameters were adjusted by ±1 standard deviation showed the importance of accurately assigning photosynthetic parameters in global and regional calculations of primary production. The assimilation number of the P-I curve showed strong relationships with environmental variables such as temperature and had a practically one-to-one relationship with the magnitude of change in primary production. In the future, such empirical relationships could potentially be used for a more dynamic assignment of photosynthetic rates in the estimation of global primary production. Relationships between the initial slope of the P-I curve and environmental variables were more elusive.

Publications

Publications (27)
Article
The chemical composition of Calanus finmarchicus was analyzed at 21 stations from three regions where 12 transects were sampled from 0 to 50 m depth, including stage composition analysis at the Siglunes and Selvogsbanki transects in relation to the effects of different water masses, during a survey in Icelandic waters during 11–29 May 2018. The sta...
Article
Full-text available
This study compares inter-annual dynamics of the two biomass dominant copepods in the Iceland Sea, the North Atlantic species Calanus finmarchicus and the Arctic C. hyperboreus, in an era of relatively low temperatures in the beginning of the study period (1990-1995) and higher temperatures thereafter. Samples were collected annually in May along a...
Article
Full-text available
Since the article “Primary Production, an Index of Climate Change in the Ocean: Satellite-Based Estimates over Two Decades” by Kulk et al. [1] was published, we discovered an error in the code of the primary production model, which crept in when the code was updated from the original version described by Platt and Sathyendranath (1988), Sathyendran...
Technical Report
Full-text available
Abstract A sampling dedicated for the project “Ecologically and economically sustainable mesopelagic fisheries” (MEESO), funded by the European Union, took place during a cruise designed to study pelagic ecosystems of the Nordic Seas during summer (IESSNS) in July 2020. The main aim of the MEESO work was to study the abundance, distribution and com...
Article
Full-text available
Primary production by marine phytoplankton is one of the largest fluxes of carbon on our planet. In the past few decades, considerable progress has been made in estimating global primary production at high spatial and temporal scales by combining in situ measurements of primary production with remote-sensing observations of phytoplankton biomass. O...
Article
Full-text available
Phenological variations of the marine copepod Calanus finmarchicus were studied in Svalbard and northern Iceland, where samples were collected in summer and spring, respectively, over two decades. Four phenological indices, developed for copepodite stage-structured data, were used: the proportion of CV to total abundance (CVT), the population devel...
Article
Full-text available
Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But the quantifica-tion and validation of ocean primary productivity at large scale remains a major challenge due to limited coverage of ship-based measurements and the difficulty of validating diverse me...
Article
Full-text available
The photosynthetic performance of marine phytoplankton varies in response to a variety of factors, environmental and taxonomic. One of the aims of the MArine primary Production: model Parameters from Space (MAPPS) project of the European Space Agency is to assemble a global database of photosynthesis–irradiance (P-E) parameters from a range of ocea...
Article
Full-text available
Fixation of organic carbon by phytoplankton is the foundation of nearly all open-ocean ecosystems and a critical part of the global carbon cycle. But quantification and validation of ocean primary productivity at large scale remains a major challenge, due to limited coverage of ship-based measurements and the difficulty of validating diverse measur...
Article
Full-text available
In the advective realm of the seas, it is challenging to disentangle the role of regional and local processes on zooplankton populations. However, comparative studies of spatially separated zooplankton populations can provide valuable insights into this issue. We studied interannual abundance variation of the key zooplankton species Calanus finmarc...
Article
Full-text available
The photosynthetic performance of marine phytoplankton varies in response to a variety of factors, environmental and taxonomic. One of the aims of the MArine primary Production: model Parameters from Space (MAPPS) project of the European Space Agency is to assemble a global database of photosynthesis-irradiance (P-E) parameters from a range of ocea...
Article
Near-surface chlorophyll a concentration is a fundamental component of marine ecological processes, and its changes reflect the phytoplankton growth (primary productivity as well as loss due to grazing and sinking) feeding into higher trophic levels. Time series of measurements from several satellite sensors since late 1997 can be used as a proxy o...
Article
While remotely sensed data greatly improves the spatial and temporal resolution of ocean surface data, many data gaps still exist, particularly in northern latitude regions. We addressed this issue by reconstructing 8-day chl-a, sea surface temperature (SST) and photosynthetically available radiation (PAR) between 1998 and 2013. Direct matchups bet...
Article
Full-text available
A 24-year time series of the abundance of Calanus finmarchicus from two standard sections differing in hydrographical conditions (Atlantic Water south of Iceland, Subarctic Water north of Iceland) was examined in relation to hydrography, phytoplankton dynamics, and large-scale climatic forcing (North Atlantic Oscillation, NAO). In the sea area arou...
Article
Full-text available
Generalized additive models (GAMs) were used to test the hypothesis that changes in physical and biological environmental conditions affected by current climatic warming would negatively impact the euphausiid populations in the North Atlantic. Two zooplankton time series were used, one collected by the Marine Research Institute (MRI) on a transect...
Article
Full-text available
We developed an ecosystem/biogeochemical model system, which includes multiple phytoplankton functional groups and carbon cycle dynamics, and applied it to investigate physical-biological interactions in Icelandic waters. Satellite and in situ data were used to evaluate the model. Surface seasonal cycle amplitudes and biases of key parameters (DIC,...
Article
Phytoplankton phenology and primary production were examined in the Iceland–Faroe region through synthesis of all available data, both in situ and remotely sensed. In the Arctic water, the early onset of stratification in spring gave rise to the rapid shallowing of the mixed layer and triggered the earlier spring bloom north of Iceland, whereas the...
Article
Full-text available
We use an ecosystem/biogeochemical model, which includes multiple phytoplankton functional groups and carbon cycle dynamics, to investigate physical-biological interactions in Icelandic waters. Satellite and in situ data were used to validate the model. The seasonality of the coccolithophore and "other phytoplankton" (diatoms and dinoflagellates) b...
Article
Full-text available
Guðmundsson, K., Heath, M. R., and Clarke, E. D. 2009. Average seasonal changes in chlorophyll a in Icelandic waters. – ICES Journal of Marine Science, 66: 2133–2140.The standard algorithms used to derive sea surface chlorophyll a concentration from remotely sensed ocean colour data are based almost entirely on the measurements of surface water sam...
Article
Full-text available
An 18 year zooplankton time series from two standard sections differing in hydrographic conditions (Subarctic Water north of Iceland and Atlantic water south of Iceland) was examined in relation to hydrography and phytoplankton dynamics, and large-scale climatic changes in the North Atlantic Ocean, particularly the North Atlantic Oscillation (NAO)....
Article
The 2008 North Atlantic Spring Bloom Experiment (NAB08) employed a system of drifting floats, mobile gliders and ship-based measurements to resolve patch-scale physical and biological variability over the 3- month course of an entire bloom. Although both autonomous and ship-based elements were essential to achieving NAB08 goals, the autonomous syst...
Article
As part of the 2008 North Atlantic Spring Bloom Experiment (NAB08), 2 Lagrangian Floats and 4 Seagliders were deployed in early April before the bloom began. Mixed-layer depth exceeded 150m; chlorophyll concentrations were low and dissolved nutrient concentrations were high; CTD profiles of chlorophyll fluorescence and optical backscattering (proxi...
Article
As part of the 2008 North Atlantic Spring Bloom Experiment (NAB08), hyperspectral radiometric and bio- optical measurements were taken from two Lagrangian Floats every 40-200 s. Measured quantities included downwelling irradiance Ed(λ,z) and upwelling radiance Lu(λ,z) from 320-950 nm as well as oxygen, chlorophyll fluorescence and two inherent opti...
Article
The 2008 North Atlantic Spring Bloom Experiment (NAB08) aimed to understand carbon export from this globally important event by combining a new generation of autonomous floats and gliders equipped with a new generation of sensors, and traditional and modern shipboard observational methods. Measurements were made from early April to late June 2008 i...
Article
Four Seagliders and two Lagrangian floats were deployed before the onset of the North Atlantic Bloom (NAB) at 59.0°N 20.5°W in early April 2008. The Seagliders surveyed around the Langrangian floats, which were designed to drift in the mixed layer and meandered northwest across the Icelandic Basin during the development of the bloom, finally becomi...
Article
Annual variations in primary productivity (uptake of 14C) measurements in Icelandic waters during spring since 1958 are analysed for four geographically defined regions, which correspond to major hydrographical features. The overall means by region range from 4.3 to 9.2 mg C m−3 h−1. Annual variation in the shelf region north-east of Iceland reflec...

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