| 1. |
- Bergström, Ulf
(författare)
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Spatio-temporal dynamics of cod nursery areas in the Baltic Sea
- 2017
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 155, s. 28-40
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Tidskriftsartikel (refereegranskat)abstract
- In this study the drift of eastern Baltic cod larvae and juveniles spawned within the historical eastern Baltic cod spawning grounds was investigated by detailed drift model simulations for the years 1971-2010, to examine the spatio-temporal dynamics of environmental suitability in the nursery areas of juvenile cod settlement. The results of the long-term model scenario runs, where juvenile cod were treated as simulated passively drifting particles, enabled us to find strong indications for long-term variations of settlement and potentially the reproduction success of the historically important eastern Baltic cod nursery grounds. Only low proportions of juveniles hatched in the Arkona Basin and in the Gotland Basin were able to settle in their respective spawning ground. Ocean currents were either unfavorable for the juveniles to reach suitable habitats or transported the juveniles to nursery grounds of neighboring subdivisions. Juveniles which hatched in the Bornholm Basin were most widely dispersed and showed the highest settlement probability, while the second highest settlement probability and horizontal dispersal was observed for juveniles originating from the Gdansk Deep. In a long-term perspective, wind-driven transport of larvae/juveniles positively affected the settlement success predominately in the Bornholm Basin and in the Bay of Gdansk. The Bornholm Basin has the potential to contribute on average 54% and the Bay of Gdansk 11% to the production of juveniles in the Baltic Sea. Furthermore, transport of juveniles surviving to the age of settlement with origin in the Bornholm Basin contributed on average 13 and 11% to the total settlement in the Arkona Basin and in the Gdansk Deep, respectively. The time-series of the simulated occupied juvenile cod habitat in the Bornholm Basin and in the Gdansk Deep showed a similar declining trend as the Fulton's K condition factor of demersal 1-group cod, which may confirm the importance of oxygen-dependent habitat availability and its effect on density dependence as a process relevant for recruitment success. (C) 2017 Elsevier Ltd. All rights reserved.
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| 2. |
- Chambault, Philippine, et al.
(författare)
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The influence of oceanographic features on the foraging behavior of the olive ridley sea turtle Lepidochelys olivacea along the Guiana coast
- 2016
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 142, s. 58-71
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Forskningsöversikt (refereegranskat)abstract
- The circulation in the Western Equatorial Atlantic is characterized by a highly dynamic mesoscale activity that shapes the Guiana continental shelf. Olive ridley sea turtles (Lepidochelys olivacea) nesting in French Guiana cross this turbulent environment during their post-nesting migration. We studied how oceanographic and biological conditions drove the foraging behavior of 18 adult females, using satellite telemetry, remote sensing data (sea surface temperature, sea surface height, current velocity and euphotic depth), simulations of micronekton biomass (pelagic organisms) and in situ records (water temperature and salinity). The occurrence of foraging events throughout migration was located using Residence Time analysis, while an innovative proxy of the hunting time within a dive was used to identify and quantify foraging events during dives. Olive ridleys migrated northwestwards using the Guiana current and remained on the continental shelf at the edge of eddies formed by the North Brazil retroflection, an area characterized by low turbulence and high micronekton biomass. They performed mainly pelagic dives, hunting for an average 77% of their time. Hunting time within a dive increased with shallower euphotic depth and with lower water temperatures, and mean hunting depth increased with deeper thermocline. This is the first study to quantify foraging activity within dives in olive ridleys, and reveals the crucial role played by the thermocline on the foraging behavior of this carnivorous species. This study also provides novel and detailed data describing how turtles actively use oceanographic structures during post-nesting migration.
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| 3. |
- Hátún, Hjálmar, et al.
(författare)
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An inflated subpolar gyre blows life toward the northeastern Atlantic
- 2016
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Ingår i: Progress in Oceanography. - 0079-6611. ; 147, s. 49-66
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Tidskriftsartikel (refereegranskat)abstract
- Deep convection in the Labrador and Irminger Seas inflates the cold and low-saline subpolar gyre, which is a rich nutrient and zooplankton source for the surrounding warmer waters of subtropical origin. The zooplankton abundances on the south Iceland shelf show characteristic sub-decadal variability, which closely reflect the oceanic abundances of the ecologically most important zooplankton species – Calanus finmarchicus. Much higher abundances of this species are observed during years when the winter mixed layer depths (MLD) in the Labrador-Irminger Sea, and over the Reykjanes Ridge are deep. Furthermore, a tight relationship is identified between on-shelf zooplankton abundances and lateral shifts of the biologically productive subarctic front southwest of Iceland. Thus, we suggest that northeastward expansion of the subpolar gyre results in biologically productive periods in the waters southwest of Iceland – both oceanic and on the shelf. In addition to local atmospheric forcing, we find that the MLD and frontal position are also impacted by remote heat losses and convection in the Labrador Sea, through northward advection of unstable mode waters. The sub-decadal oceanic and on-shelf biological production peaks are possibly predictable by half a year (local winter convection to subsequent summer production), and the advective time-lag from the Labrador Sea might induce an even longer predictability horizon (up to 1.5 years).
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| 4. |
- Hinrichsen, H-H, et al.
(författare)
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Spawning areas of eastern Baltic cod revisited : Using hydrodynamic modelling to reveal spawning habitat suitability, egg survival probability, and connectivity patterns
- 2016
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 143, s. 13-25
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Forskningsöversikt (refereegranskat)abstract
- In the highly variable environment of the Baltic Sea two genetically distinct cod stocks exist, one west of the island of Bornholm, which is referred to as the western stock, and one to the east of Bornholm, the eastern stock. A hydrodynamic model combined with a Lagrangian particle tracking technique was utilised to provide spatially and temporally resolved long-term information on environmentally-related (i) spawning habitat size, (ii) egg/yolk-sac larval survival, (iii) separation of causes of mortality, and (iv) connectivity between spawning areas of eastern Baltic cod. Simulations were performed to quantify processes generating heterogeneity in spatial distribution of cod eggs and yolk sac larvae up to the first feeding stage. The spatial extent of cod eggs represented as virtual drifters is primarily determined by oxygen and salinity conditions at spawning, which define the habitat requirement to which cod's physiology is suited for egg development. The highest habitat suitability occurred in the Bornholm Basin, followed by the Gdansk Deep, while relatively low habitat suitability was obtained for the Arkona and the Gotland Basin. During drift egg and yolk sac larval survival is to a large extent affected by sedimentation. Eggs initially released in the western spawning grounds (Arkona and Bornholm Basin) were more affected by sedimentation than those released in the eastern spawning grounds (Gdansk Deep and Gotland Basin). Highest relative survival of eastern Baltic cod eggs occurred in the Bornholm Basin, with a pronounced decrease towards the Gdansk Deep and the Gotland Basin. Relatively low survival rates in the Gdansk Deep and in the Gotland Basin were attributable to oxygen-dependent mortality. Low oxygen content had almost no impact on survival in the Arkona Basin. For all spawning areas temperature dependent mortality was only evident after severe winters. Egg buoyancy in relation to topographic features like bottom sills and strong bottom slopes could appear as a barrier for the transport of Baltic cod eggs and yolk sac larvae and could potentially limit the connectivity of Baltic cod early life stages between the different basins in the western and eastern Baltic Sea. The possibility of an eastward directed transport up to the first-feeding larval stage exists only for eggs and yolk sac larvae at high buoyancy levels, suggesting that dispersal of early life stages between these spawning areas is limited.
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| 5. |
- Labrousse, Sara, et al.
(författare)
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Winter use of sea ice and ocean water mass habitat by southern elephant seals : The length and breadth of the mystery
- 2015
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611 .- 1873-4472. ; 137, s. 52-68
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Forskningsöversikt (refereegranskat)abstract
- Understanding the responses of animals to the environment is crucial for identifying critical foraging habitat. Elephant seals (Mirounga leonine) from the Kerguelen Islands (49 degrees 20'S, 70 degrees 20'E) have several different foraging strategies. Why some individuals undertake long trips to the Antarctic continent while others utilize the relatively close frontal zones is poorly understood. Here, we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals (SES). To do this, we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive, low resolution dataset from CTD-Satellite Relay Data Loggers (CTD-SRDLs). A sample of 37 post-breeding SES females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events (PEE) to dive parameters (dive duration, bottom duration, hunting-time, maximum depth, ascent speed, descent speed, sinuosity, and horizontal speed) for each strategy. We applied these models to a second sample of 35 seals, 20 males and 15 females, during the post-moult foraging trip to the Antarctic continental shelf between 2004 and 2013, which did not have fine-scale behavioural data. The females were widely distributed with important foraging activity south of the Southern Boundary Front, while males predominately travelled to the south-eastern part of the East Antarctica region. Combining our predictions of PEE with environmental features (sea ice concentration, water masses at the bottom phase of dives, bathymetry and slope index) we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying Antarctic Surface Water (AASW) and the underlying Modified Circumpolar Deep Water (MCDW). Increased biological activity associated with the upper boundary of MCDW, may provide overwintering areas for SES prey. Male foraging activity was strongly associated with pelagic dives within the Antarctic Slope Front where upwelling of nutrient rich Circumpolar Deep Water onto surface water may enhance and concentrate resources. A positive association between sea ice and foraging activity was found for both sexes where increased biological activity may sustain an under-ice ecosystem. Variability of the East Antarctic sea ice season duration is likely a crucial element to allow air-breathing predators to benefit from profitable prey patches within the pack ice habitat.
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| 6. |
- Linders, Johanna, et al.
(författare)
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On the nature and origin of water masses in Herald Canyon, Chukchi Sea: Synoptic surveys in summer 2004, 2008, and 2009
- 2017
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 159, s. 99-114
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Tidskriftsartikel (refereegranskat)abstract
- Hydrographic and velocity data from three high-resolution shipboard surveys of Herald Canyon in the northwest Chukchi Sea, in 2004, 2008, and 2009, are used to investigate the water masses in the canyon and their possible source regions. Both summer and winter Pacific waters were observed in varying amounts in the different years, although in general the summer waters resided on the eastern side of the canyon while the winter waters were located on the western flank. The predominant summer water was Bering summer water, although some Alaskan coastal water resided in the canyon in the two later years likely due to wind forcing. Both newly ventilated and remnant winter waters were found in the canyon, but the amount lessened in each successive survey. Using mooring data from Bering Strait it is shown that a large amount of Bering summer water in the western channel of the strait follows a relatively direct route into Herald Canyon during the summer months, with an estimated advective speed of 10–20 cm/s. However, while the winter water observed in 2004 was consistent with a Bering Strait source (with a slower advective speed of 5–8 cm/s), the dense water in the canyon during 2008 and 2009 was more in line with a northern source. This is consistent with sections to the west of the canyon and with previously reported measurements implying winter water formation on the East Siberian shelf. Large-scale wind patterns and polynya activity on the shelf are also investigated. It was found that the former appears to impact more strongly the presence of dense water in Herald Canyon. © 2017 Elsevier Ltd
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| 7. |
- Pinones, A., et al.
(författare)
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Hydrographic variability along the inner and mid-shelf region of the western Ross Sea obtained using instrumented seals
- 2019
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 174, s. 131-142
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Tidskriftsartikel (refereegranskat)abstract
- Temperature and salinity measurements obtained from sensors deployed on Weddell seals (Leptonychotes weddellii) between late austral summer and the following spring for 2010-2012 were used to describe the temporal and spatial variability of hydrographic conditions in the western Ross Sea, with particular emphasis on the inner-shelf region off Victoria Land and McMurdo Sound. Potential temperature-salinity diagrams constructed for regions where the seals remained for extended periods showed four water masses on the continental shelf: Modified Circumpolar Deep Water, Antarctic Surface Water, Shelf Water and Modified Shelf Water. Depth-time distributions of potential density and buoyancy frequency showed the erosion of the upper water column stratification associated with the transition from summer to fall/winter conditions. The within-year and interannual variability associated with this transition was related to wind speed. Changes in upper water column density were positively correlated with cross-shelf wind speeds > 5.5 m s(-1) with a 3-4 day lag. A range of wind speeds was required to erode the density structure because of different levels of stratification in each year. A comparison of wind mixing potential versus stratification (Wedderburn number) showed that synoptic scale wind events during 2012 with speeds of 5.5 and 6.5 m s(-1) were needed to erode the summer stratification for Ross Island and Victoria Land regions, respectively. Stronger winds ( > 8.5 m s(-1) ) were required during 2010 and 2011. The interannual variability in total heat content accumulated during summer (about 20%) was related to the duration of open water, with the largest heat content occurring in 2012, which was characterized by a summer sea ice minimum stronger than other years and relatively higher mCDW influence over the mid and outer-shelf regions. The heat content was lost after mid-April and reached a minimum in winter as a result of deep winter convection. The quantitative analysis of hydrographic variability of the inner-shelf region of the western Ross Sea obtained from the seal-derived measurements provides a baseline for assessing future changes.
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| 8. |
- Swalethorp, Rasmus, et al.
(författare)
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Microzooplankton distribution in the Amundsen Sea Polynya (Antarctica) during an extensive Phaeocystis antarctica bloom
- 2019
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Ingår i: Progress in Oceanography. - : Elsevier. - 0079-6611 .- 1873-4472. ; 170, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- In Antarctica, summer is a time of extreme environmental shifts resulting in large coastal phytoplankton blooms fueling the food web. Despite the importance of the microbial loop in remineralizing biomass from primary production, studies of how microzooplankton communities respond to such blooms in the Southern Ocean are rather scarce. Microzooplankton (ciliate and dinoflagellate) communities were investigated combining microscopy and 18S rRNA sequencing analyses in the Amundsen Sea Polynya during an extensive summer bloom of Phaeocystis antarctica. The succession of microzooplankton was further assessed during a 15-day induced bloom microcosm experiment. Dinoflagellates accounted for up to 59 % of the microzooplankton biomass in situ with Gymnodinium spp., Protoperidiwn spp. and Gyrodinium spp. constituting 89 % of the dinoflagellate biomass. Strobilidium spp., Strombidium spp. and tintinids represented 90 % of the ciliate biomass. Gymnodiniwn, Gyrodinium and tintinnids are known grazers of Phaeocystis, suggesting that this prymnesiophyte selected for the key microzooplankton taxa. Availability of other potential prey, such as diatoms, heterotrophic nanoflagellates and bacteria, also correlated to changes in microzooplankton community structure. Overall, both heterotrophy and mixotrophy appeared to be key trophic strategies of the dominant microzooplankton observed, suggesting that they influence carbon flow in the microbial food web through top-down control on the phytoplankton community.
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| 9. |
- Taucher, Jan, et al.
(författare)
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In situ camera observations reveal major role of zooplankton in modulating marine snow formation during an upwelling-induced plankton bloom
- 2018
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Ingår i: Progress in Oceanography. - : Elsevier. - 0079-6611 .- 1873-4472. ; 164, s. 75-88
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Tidskriftsartikel (refereegranskat)abstract
- Particle aggregation and the consequent formation of marine snow alter important properties of biogenic particles (size, sinking rate, degradability), thus playing a key role in controlling the vertical flux of organic matter to the deep ocean. However, there are still large uncertainties about rates and mechanisms of particle aggregation, as well as the role of plankton community structure in modifying biomass transfer from small particles to large fast-sinking aggregates.Here we present data from a high-resolution underwater camera system that we used to observe particle size distributions and formation of marine snow (aggregates >0.5 mm) over the course of a 9-week in situ mesocosm experiment in the Eastern Subtropical North Atlantic. After an oligotrophic phase of almost 4 weeks, addition of nutrient-rich deep water (650 m) initiated the development of a pronounced diatom bloom and the subsequent formation of large marine snow aggregates in all 8 mesocosms. We observed a substantial time lag between the peaks of chlorophyll a and marine snow biovolume of 9–12 days, which is much longer than previously reported and indicates a marked temporal decoupling of phytoplankton growth and marine snow formation during our study. Despite this time lag, our observations revealed substantial transfer of biomass from small particle sizes (single phytoplankton cells and chains) to marine snow aggregates of up to 2.5 mm diameter (ESD), with most of the biovolume being contained in the 0.5–1 mm size range. Notably, the abundance and community composition of mesozooplankton had a substantial influence on the temporal development of particle size spectra and formation of marine snow aggregates: While higher copepod abundances were related to reduced aggregate formation and biomass transfer towards larger particle sizes, the presence of appendicularia and doliolids enhanced formation of large marine snow.Furthermore, we combined in situ particle size distributions with measurements of particle sinking velocity to compute instantaneous (potential) vertical mass flux. However, somewhat surprisingly, we did not find a coherent relationship between our computed flux and measured vertical mass flux (collected by sediment traps in 15 m depth). Although the onset of measured vertical flux roughly coincided with the emergence of marine snow, we found substantial variability in mass flux among mesocosms that was not related to marine snow numbers, and was instead presumably driven by zooplankton-mediated alteration of sinking biomass and export of small particles (fecal pellets).Altogether, our findings highlight the role of zooplankton community composition and feeding interactions on particle size spectra and formation of marine snow aggregates, with important implications for our understanding of particle aggregation and vertical flux of organic matter in the ocean.
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| 10. |
- Tremblay, J. E., et al.
(författare)
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Global and regional drivers of nutrient supply, primary production and CO2 drawdown in the changing Arctic Ocean
- 2015
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Ingår i: Progress in Oceanography. - : Elsevier BV. - 0079-6611. ; 139, s. 171-196
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Tidskriftsartikel (refereegranskat)abstract
- The main environmental factors driving spatial patterns, variability and change in primary production (PP) in the Arctic Ocean are reviewed. While instantaneous PP rates are predominantly influenced by the local factors affecting light penetration through clouds, sea ice and water, net PP (NPP) at the annual scale is conditioned by a hierarchy of remote and local processes that affect nutrient supply and light availability in general. Nutrient supply sets spatial differences in realized or potential trophic status (i.e. oligotrophic or eutrophic), whereas light availability modulates PP within each regime. Horizontal nutrient supply through Atlantic and Pacific ocean gateways differ markedly, which is explained by their position at opposite ends of the global meridional overturning circulation and imbalanced nitrogen (N) cycling in the Pacific sector. Nutrient supply by rivers is locally important, but does not appear to sustain a major portion of overall pan-Arctic NPP so far. Horizontal nutrient inputs to the surface Arctic Ocean are eventually transferred to the halocline through winter convection and the decomposition of settling organic matter. The subsequent re-injection of these nutrients to the euphotic zone varies by two orders of magnitude across sectors, depending on the strength and persistence of the vertical stratification. Such differences in nutrient delivery are commensurate with those of PP and NPP rates. Widespread N deficiency in surface waters fosters the occurrence and seasonal persistence of subsurface layers of maximum chlorophyll a (SCM) and phytoplankton carbon biomass in several sectors. The contribution of these layers to NPP is possibly higher in the Arctic than in thermally-stratified waters of the subtropical gyres due to a combination of extreme acclimation to low light and a shallow nitracline in the former. The overall impacts of SCM layers on biogeochemical fluxes remain to be quantified directly, both regionally and at the pan-Arctic scale. While CO2 intake by the Arctic Ocean should respond positively to reduced sea-ice extent, which facilitates air-sea exchange, the negative influence of rising temperatures and runoff on CO2 solubility might counteract the positive effect of modest PP increases in seasonally open waters. Overall, this review shows that local changes in light availability resulting from reduced sea-ice is only one factor in the intricate web of local and remote drivers of PP and CO2 drawdown in the Arctic Ocean. Understanding and predicting change requires an integrated biogeochemical approach that connects the small Arctic Ocean to adjacent ones and adequately resolves vertical nutrient supply processes at regional and local scales. (C) 2015 Published by Elsevier Ltd.
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