... Paper handled by associate editor Pete Hollings. ... R. Garrison, M. Greenberg, E. Herrera Pa... more ... Paper handled by associate editor Pete Hollings. ... R. Garrison, M. Greenberg, E. Herrera Paz, P. Hill, M. Ibaraki, M. Kastner, AES Kemp, K. Kvenvolden, R. Langridge, N. Lindsley-Griffin, J. Marseters, E. Martini, R. McCabe, L. Ocola, J. Resig, AW Sanchez Fernandez, HJ Schrader ...
The Northern Hemisphere sea ice record of the last decades shows large amplitude changes, which c... more The Northern Hemisphere sea ice record of the last decades shows large amplitude changes, which can be associated to the global warming. However, the anomalies also show regional patterns, which illustrate the importance of atmosphere and ocean dynamics in the distribution of sea ice. Beyond satellite observations, proxy data such as those provided by dinocyst assemblages permit to extent the record of sea ice back in time. Sea ice reconstructions spanning the last millennia are now available at several sites of the Arctic Ocean and subarctic seas (Fram Strait, Baffin Bay, Canadian Arctic Archipelago channels, Beaufort Sea and Chukchi Sea). The data illustrate large amplitude temporal trends but more importantly, opposite trends between the eastern and western Arctic. In particular, the results show a clear mid-Holocene to recent cooling accompanied with sea ice increase in the northern Baffin Bay and eastern Fram Strait. This contrasts with the changes recorded in the western part of the Canadian Arctic and Chukchi Sea, where a warming trend towards the late Holocene is accompanied with a decrease in the sea ice cover. In addition, when suitable resolution is achieved, the results indicate large amplitude centennial to millennial scale oscillations of sea-surface conditions and sea- ice cover, pointing to complex atmosphere/ocean interactions, at regional scale, in the Arctic.
A qualitative and quantitative study of recent organic-walled dinoflagellate dinocysts recovered ... more A qualitative and quantitative study of recent organic-walled dinoflagellate dinocysts recovered in sediments has been undertaken in the coastal zone of the Gulf of Tehuantepec, Mexico. A sediment core was collected in 2004 with a Reineck-type corer using a plastic tube (7 cm i.d); and it was subsampled at 0.3 cm intervals down to 10 cm depth and then at 1 cm intervals at further depths. The 210Pb and 137Cs-derived sedimentation and mass accumulation rates at the site were found to vary from 0.033 to 0.209 cm yr-1, and from 0.05 to 0.29 g cm-2 yr-1., respectively. The cysts concentrations ranged between 477 and 2300 cysts g-1 and the cysts fluxes between 68 a 494 cysts cm-2 yr-1. Twenty-three cyst taxa were identified: Brigantedinium spp., Polysphaeridium zoharyii, Bitectatodinium spongium, Spiniferites delicatus, Quinquecuspis concreta, Echinidinium transparantum, Operculodinium centrocarpum, Selenopemphix quanta, Type Echinidinium granulatum, Echinidinium aculeatum, Protoperidinium americanum, Echinidinium delicatum, Selenopemphix nephroides, Cyst of Protoperidinum stellatum, Lingulodinium machaerophorum, Islandinium spp., Votadinium spinosum, Polykrikos kofoidii, Pentapharsodinium dalei, Tuberculodinium vancampoe, Spiniferites mirabilis, Votadinium calvum and Nematosphaeropsis labyrinthus. The assemblages included cysts of both phototrophic and heterotrophic species, with variation of their respective abundance reflecting changes in the trophic structure of the upper water mass, especially after 1950, with a decrease from ~30% to 15% of photototrophic species, likely as a response to pollution (including cultural eutrophication) created by the industrial development of the adjacent coastal zone. Brigantedinium spp., Polysphaeridium zoharyii and Bitectatodinium spongium, were the dominant species found in the core and are most likely influenced by the seasonal upwelling that characterize the study area, as indicated by the predominance of planktonic foraminiferal species Globigerina bulloides and Globigerinita glutinata throughout the core. Potentially toxic species such as Polysphaeridium zohary (cyst of Pyrodinium bahamense var. compressum) were also observed all along the sediment core and new analysis are to be performed to further investigate their presence in the zone.
In order to develop a proxy of past productivity, we explored the relationship between the assemb... more In order to develop a proxy of past productivity, we explored the relationship between the assemblages of organic- walled dinoflagellate cysts (or dinocysts) in marine sediment and productivity estimated from remote sensing. Dinoflagellates represent an important part of the primary production in the ocean. Their populations, which include both phototrophic and heterotrophic taxa, depend upon the trophic structure of upper water masses. Here, we used dinocyst data from 1171 surface sediment samples collected in the North Atlantic, Arctic and North Pacific oceans. For each sample site, we compiled two sets of primary productivity data derived from satellite observations: (1) The dataset from the Coastal Zone Color Scanner (CZCS) program applied to observations from 1978 to 1989 and (2) the data set from the MODerate resolution Imaging Spectroradiometer (MODIS) program using observations from 2002 to 2005. Canonical correspondence analyses (CCA) were performed with 57 dinocyst taxa and 8 sea-surface parameters (winter and summer salinity, winter and summer temperature, sea-ice cover, summer, winter and annual primary productivity). Results show that primary productivity is significantly correlated with the first or second component of dinocyst assemblages, depending upon the ocean basin considered, with the strongest relation being observed in the North Pacific. We tested the modern analogue technique (MAT) for quantitative reconstruction of productivity using dinocysts. The error of prediction is ±15-25 % depending upon the productivity dataset, with the best performance obtained for winter productivity using the MODIS data. It is noteworthy that the error of prediction for all estimated productivity parameters is lower than the differences between productivity data derived from the MODIS and CZCS datasets. Therefore, we conclude that dinocysts can be used to reconstruct productivity with reliability as good as possible given the uncertainty inherent to primary productivity estimates from satellite observations. MAT has been applied to northern North Atlantic time series, with special attention paid to the last glacial maximum (LGM). The reconstructions using MODIS and CZCS datasets indicates generally low productivity during the glacial stage, especially during the Younger Dryas and Heinrich events, with annual productivity of less than 100 gC m-2. Past productivity estimates for the LGM are consistent with simulation of the North Atlantic Ocean productivity in the hypothesis of reduced Atlantic Meridional Overturning as proposed by Schmittner (Nature, 2005) based on coupled climate-ecosystem model simulation.
... Paper handled by associate editor Pete Hollings. ... R. Garrison, M. Greenberg, E. Herrera Pa... more ... Paper handled by associate editor Pete Hollings. ... R. Garrison, M. Greenberg, E. Herrera Paz, P. Hill, M. Ibaraki, M. Kastner, AES Kemp, K. Kvenvolden, R. Langridge, N. Lindsley-Griffin, J. Marseters, E. Martini, R. McCabe, L. Ocola, J. Resig, AW Sanchez Fernandez, HJ Schrader ...
The Northern Hemisphere sea ice record of the last decades shows large amplitude changes, which c... more The Northern Hemisphere sea ice record of the last decades shows large amplitude changes, which can be associated to the global warming. However, the anomalies also show regional patterns, which illustrate the importance of atmosphere and ocean dynamics in the distribution of sea ice. Beyond satellite observations, proxy data such as those provided by dinocyst assemblages permit to extent the record of sea ice back in time. Sea ice reconstructions spanning the last millennia are now available at several sites of the Arctic Ocean and subarctic seas (Fram Strait, Baffin Bay, Canadian Arctic Archipelago channels, Beaufort Sea and Chukchi Sea). The data illustrate large amplitude temporal trends but more importantly, opposite trends between the eastern and western Arctic. In particular, the results show a clear mid-Holocene to recent cooling accompanied with sea ice increase in the northern Baffin Bay and eastern Fram Strait. This contrasts with the changes recorded in the western part of the Canadian Arctic and Chukchi Sea, where a warming trend towards the late Holocene is accompanied with a decrease in the sea ice cover. In addition, when suitable resolution is achieved, the results indicate large amplitude centennial to millennial scale oscillations of sea-surface conditions and sea- ice cover, pointing to complex atmosphere/ocean interactions, at regional scale, in the Arctic.
A qualitative and quantitative study of recent organic-walled dinoflagellate dinocysts recovered ... more A qualitative and quantitative study of recent organic-walled dinoflagellate dinocysts recovered in sediments has been undertaken in the coastal zone of the Gulf of Tehuantepec, Mexico. A sediment core was collected in 2004 with a Reineck-type corer using a plastic tube (7 cm i.d); and it was subsampled at 0.3 cm intervals down to 10 cm depth and then at 1 cm intervals at further depths. The 210Pb and 137Cs-derived sedimentation and mass accumulation rates at the site were found to vary from 0.033 to 0.209 cm yr-1, and from 0.05 to 0.29 g cm-2 yr-1., respectively. The cysts concentrations ranged between 477 and 2300 cysts g-1 and the cysts fluxes between 68 a 494 cysts cm-2 yr-1. Twenty-three cyst taxa were identified: Brigantedinium spp., Polysphaeridium zoharyii, Bitectatodinium spongium, Spiniferites delicatus, Quinquecuspis concreta, Echinidinium transparantum, Operculodinium centrocarpum, Selenopemphix quanta, Type Echinidinium granulatum, Echinidinium aculeatum, Protoperidinium americanum, Echinidinium delicatum, Selenopemphix nephroides, Cyst of Protoperidinum stellatum, Lingulodinium machaerophorum, Islandinium spp., Votadinium spinosum, Polykrikos kofoidii, Pentapharsodinium dalei, Tuberculodinium vancampoe, Spiniferites mirabilis, Votadinium calvum and Nematosphaeropsis labyrinthus. The assemblages included cysts of both phototrophic and heterotrophic species, with variation of their respective abundance reflecting changes in the trophic structure of the upper water mass, especially after 1950, with a decrease from ~30% to 15% of photototrophic species, likely as a response to pollution (including cultural eutrophication) created by the industrial development of the adjacent coastal zone. Brigantedinium spp., Polysphaeridium zoharyii and Bitectatodinium spongium, were the dominant species found in the core and are most likely influenced by the seasonal upwelling that characterize the study area, as indicated by the predominance of planktonic foraminiferal species Globigerina bulloides and Globigerinita glutinata throughout the core. Potentially toxic species such as Polysphaeridium zohary (cyst of Pyrodinium bahamense var. compressum) were also observed all along the sediment core and new analysis are to be performed to further investigate their presence in the zone.
In order to develop a proxy of past productivity, we explored the relationship between the assemb... more In order to develop a proxy of past productivity, we explored the relationship between the assemblages of organic- walled dinoflagellate cysts (or dinocysts) in marine sediment and productivity estimated from remote sensing. Dinoflagellates represent an important part of the primary production in the ocean. Their populations, which include both phototrophic and heterotrophic taxa, depend upon the trophic structure of upper water masses. Here, we used dinocyst data from 1171 surface sediment samples collected in the North Atlantic, Arctic and North Pacific oceans. For each sample site, we compiled two sets of primary productivity data derived from satellite observations: (1) The dataset from the Coastal Zone Color Scanner (CZCS) program applied to observations from 1978 to 1989 and (2) the data set from the MODerate resolution Imaging Spectroradiometer (MODIS) program using observations from 2002 to 2005. Canonical correspondence analyses (CCA) were performed with 57 dinocyst taxa and 8 sea-surface parameters (winter and summer salinity, winter and summer temperature, sea-ice cover, summer, winter and annual primary productivity). Results show that primary productivity is significantly correlated with the first or second component of dinocyst assemblages, depending upon the ocean basin considered, with the strongest relation being observed in the North Pacific. We tested the modern analogue technique (MAT) for quantitative reconstruction of productivity using dinocysts. The error of prediction is ±15-25 % depending upon the productivity dataset, with the best performance obtained for winter productivity using the MODIS data. It is noteworthy that the error of prediction for all estimated productivity parameters is lower than the differences between productivity data derived from the MODIS and CZCS datasets. Therefore, we conclude that dinocysts can be used to reconstruct productivity with reliability as good as possible given the uncertainty inherent to primary productivity estimates from satellite observations. MAT has been applied to northern North Atlantic time series, with special attention paid to the last glacial maximum (LGM). The reconstructions using MODIS and CZCS datasets indicates generally low productivity during the glacial stage, especially during the Younger Dryas and Heinrich events, with annual productivity of less than 100 gC m-2. Past productivity estimates for the LGM are consistent with simulation of the North Atlantic Ocean productivity in the hypothesis of reduced Atlantic Meridional Overturning as proposed by Schmittner (Nature, 2005) based on coupled climate-ecosystem model simulation.
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