The transition from the last ice age to the present-day interglacial was interrupted by the Young... more The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more highresolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0–10.2kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate.
A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studi... more A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studied to investigate changes in sea surface conditions in the fjord during the last 60 years (1953–2014). The diatom-based reconstruction of August sea surface temperature (aSST) demonstrates a clear warming trend of 0.6 °C through the record. As inferred from Marginal Ice Zone (MIZ) diatoms, surface warming occurs in parallel with a decline in sea ice extent (SIE) during recent decades. Factor analysis identified variations in diatom assemblages representing different water masses, showing a dominance of Arctic water diatoms throughout the period and decadal variations in the sea ice assemblage during periods of peak sea ice extent. The strong dominance of Arctic water diatoms along with increasing aSST suggest prolonged open-water conditions and increased sea ice melting in the region throughout the observed period. The reconstructed ocean surface changes are in line with the background warming occurring over the Arctic region. A comparison with instrumental records from neighboring regions supports the quality of the reconstructions, including the average reconstructed aSST and the magnitude of the warming trend. We suggest that increased CO2 forcing together with ocean–atmospheric interaction have caused the increasing SST trend and decreasing sea ice presence in Krossfjorden rather than an increasing influence from Atlantic Water, which has amplified changes in many regions of Svalbard.
Sea surfaces temperatures (SSTs) are generated from a 1000-year-long sediment core from the easte... more Sea surfaces temperatures (SSTs) are generated from a 1000-year-long sediment core from the eastern flank of Reykjanes Ridge in the subpolar North Atlantic with a time resolution of 2-10 years. 54.3 cm long box core (Rapid 21-12B) and 370 cm long gravity core (RAPID 21-3K) were recovered from deep-sea sediments (2630 m water depth) during the RRS Charles Darwin cruise 159 in 2004. The box core is dated using the 210Pb method and it is continuously subsampled and investigated at 0.5 cm intervals for the last 230 years with a two years average time resolution. The gravity core is dated 14C AMS method and it is investigated continuously at 1.0 cm intervals with a ten years average resolution for the interval representing 230-1000 cal. years BP. August SSTs are reconstructed using marine planktonic diatom species with the Weighted Averages - Partial Least Squares (WA-PLS) method. Results achieved from the box core indicate August SST warming of c. 1 °C from 1773 AD to the present. The i...
ABSTRACT A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assem... more ABSTRACT A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a marine sediment core Rapid 21-COM recovered in the Iceland Basin (northern subpolar North Atlantic). The record has a resolution of 2-10 years for interval 800-2004 AD representing the best resolved diatom SST reconstruction from the subpolar North Atlantic for this period, and 40 years for interval 800 BC-800 AD. The record is compared with the high-resolution (4-20 years) aSST record from core CR948/2011 from the Vøring Plateau, in the Norwegian Sea, to explore the variability of the aSST gradient between these areas during the late Holocene. The two aSST records show persistent opposite climate trends toward warming in the subpolar North Atlantic and cooling in the Norwegian Sea throughout the late Holocene. The wavelet analysis reveals an apparent tendency to coherent antiphased aSST variations between the sites for the shorter time scales too, implying a possible aSST seesaw between the northern subpolar North Atlantic and the Norwegian Sea to operate during the late Holocene. At the multicentennial scale of aSST variability of 600-900 years, the records are nearly in antiphase with warmer (colder) periods in the subpolar North Atlantic corresponding to the colder (warmer) periods in the Norwegian Sea. At the shorter time scale of 200-450 years the records display a nearly phase-locked behaviour with a tendency for the positive aSST anomalies in the Norwegian Sea to lead by ca. 30 years the negative aSST anomalies in the subpolar North Atlantic. This aSST seesaw might have had a strong effect, or be associated, with the two major climate anomalies in the northwest Europe during the past Millennium: Medieval Warm Period (MWP) and the Little Ice Age (LIA). During the MWP warming of the sea surface in the Norwegian Sea occurred in parallel with cooling in the northern subpolar North Atlantic, whereas the opposite pattern emerged during the LIA. Coupled changes in aSST between the northern subpolar North Atlantic and the Norwegian Sea may indicate common driving forces behind the observed variability. The emerging spatial pattern of aSST resembles the one predicted by some modelling studies and is associated with changes in the regimes of the North Atlantic overturning circulation (AMOC). The observed aSST seesaw between the subpolar North Atlantic and the Norwegian Sea could be a surface expression of the variability of the eastern and western branches of the AMOC with a possible amplification through atmospheric feedback.
ABSTRACT The Arctic region has undergone very rapid changes in the past 50 years. Climate models ... more ABSTRACT The Arctic region has undergone very rapid changes in the past 50 years. Climate models predict accelerating rates of change in the Arctic and long-term perspectives on natural climate variability are therefore needed to understand these changes and their further effects. We used marine fossil diatom assemblages from Baffin Bay to investigate August sea surface temperatures (aSSTs) and sea ice variability during the last two millennia. The Baffin Bay area is sensitive to changes in the climate system due to its location, where it is influenced by Atlantic and Arctic water masses. The top most 77 cm of a 600 cm long marine sediment core (GeoTü SL-170) was used for a high resolution study of quantitative SST and sea ice reconstructions based on fossil marine planktonic diatoms. A calibration dataset consisting of 155 surface samples from the North Atlantic and a new set of 24 surface samples from Baffin Bay with 52 diatom species was utilized to convert diatom counts to aSSTs using the weighted averaging partial least squares (WA-PLS) transfer function method. The sea ice reconstruction was based on a qualitative method for specific diatom assemblages and quantitative sea ice reconstructions for the May sea ice cover based on the Maximum likelihood (ML) transfer function method. The age model for the core is based on the 14C method. Our data shows a slight warming trend of the surface waters in Baffin Bay for the last ca. 2 kyr. The most dominating diatom species is Thalassiosira gravida spores, which represents typical "Baffin Current assemblage". The highest aSSTs occurred during the Medieval Warm Period (MWP), presumably due to the increased advection of warm Atlantic water from the West Greenland Current into Baffin Bay. After the MWP, the sediment was poor in diatoms during the Little Ice Age (LIA) suggesting that the study area was covered by sea ice also in the summertime.
August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated from a 2... more August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated from a 230-year-long sediment core (Rapid 21-12B), from the southern limb of the Gardar Drift on the eastern flank of the Reykjanes Ridge in the subpolar North Atlantic. The reconstructed record has two years average resolution and represents the highest resolution diatom SST reconstruction from the subpolar North Atlantic. The results indicate a warming trend of ~0.5 °C of the surface waters in the Reykjanes Ridge area for the last 230 years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1 °C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860-1880 represents the warmest period during the last 230 years. The last 25 years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. Results suggest that the wind driven variations in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed aSST trends, because the aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. Their relationship however is negative. On the long time scale, the aSST record shows an increasing (warming) trend, whereas the aNAO index shows a decreasing trend. On the multidecadal scale, smoothed records show warm aSST periods during the negative aNAO trends and cold aSSTs during the positive aNAO trends. This suggests that the strong westerlies during the positive aNAO phase drive the main part of the Atlantic surface water towards north. During the negative aNAO phase, the westerly winds over the Atlantic are weakened and could cause a remarkable increase in the westwards flowing warm Atlantic water across the Reykjanes Ridge area. The observed relationship between aSST and the aNAO, however, does not hold for the most recent period from the 1960s onwards, where aSSTs and the aNAO show co-phased variations at a decadal scale. This change in the observed SST/NAO system may be caused by the anthropogenic forcing and/or global warming.
The ‘Antrea Net Find’, found in 1913 in Korpilahti on the Karelian Isthmus, is one of the most im... more The ‘Antrea Net Find’, found in 1913 in Korpilahti on the Karelian Isthmus, is one of the most important archaeological discoveries in Finland. For a long time, it was the oldest dated net find in Europe. New sediment samples were taken from the assumed find spot in 1998. The original net material and the new sediment sequence around the find spot were re-investigated using modern physical and palaeoecological techniques. They included AMS radiocarbon dates from the net material and the sediment above the find, as well as lithostratigraphical and isotope analyses from the surrounding sediment sequence. Also the material of the net cord was investigated. The palaeoenvironment of the Korpilahti area around the time of the event was reconstructed using modern biostratigraphical diatom and pollen methods. The ‘Antrea Net Find’ was recovered from the uppermost part of silty clay gyttja. The AMS radiocarbon date of the net yielded an age of 9140±135 BP. The net cord has been made of willo...
A prominent characteristic of the reconstructed Northern Hemisphere temperature signal over the l... more A prominent characteristic of the reconstructed Northern Hemisphere temperature signal over the last millennium is the transition from the Medieval Climate Anomaly to the Little Ice Age (LIA). Here we report indications for a non-linear regime shift in the North Atlantic ocean circulation at the onset of the LIA. Specifically, we apply a novel statistical test based on horizontal visibility graphs to two ocean sediment August sea-surface temperature records from the Norwegian Sea and the central subpolar basin and find robust indications of time-irreversibility in both records during the LIA onset. Despite a basin-wide cooling trend, we report an anomalous warming in the central subpolar basin during the LIA that is reproduced in ensemble simulations with the climate model of intermediate complexity CLIMBER-3α as a result of a non-linear regime shift in the subpolar North Atlantic ocean circulation. The identified volcanically triggered non-linear transition in the model simulations...
ABSTRACT The classical Maximum Density data of 65 Torneträsk trees from years 441 to 1980 AD are ... more ABSTRACT The classical Maximum Density data of 65 Torneträsk trees from years 441 to 1980 AD are studied in millennial, centennial and volcanic scales. The millennial scale is analyzed applying a specific filtering method. In that scale, the climate is cool after 1200–1400 AD. This more or less steady period is suggested to be due to volcanic episodes, which reduced the northward heat transport in the North Atlantic. The century scale variation, on the other hand, is suggested to be due to internal oscillations in sea surface temperature (SST) and to be connected to variations in the Arctic sea ice. Specifically, these oscillations have caused an additional warming and cooling trend in Northern Fennoscandian temperatures before and after 1930's, respectively. Variations in the temperature estimates are explained by the results for different temporal scales. All of them show local impacts leading to differences when compared with hemispheric estimates. The long-term estimate of the temperature as derived from the present Torneträsk data is found to be biased. The source of that is unknown.
ABSTRACT Preservation of diatoms in sediments of the North Atlantic and Arctic Ocean through geol... more ABSTRACT Preservation of diatoms in sediments of the North Atlantic and Arctic Ocean through geological time has been highly variable. The North Atlantic Ocean and the Nordic Seas were a region of high productivity of biogenic silica until the onset of Northern Hemisphere glaciations during the late Miocene. Later, fluctuating Pleistocene climatic conditions had a major impact on diatom productivity in the high latitude North Atlantic. During interglacials high diatom productivity took place in the North Atlantic, whereas glacial stages are often barren of diatoms due to the expansion of sea ice cover. Diatom species show rapid evolution through time and therefore are an excellent biostratigraphic tool in this area. The high diversity of diatoms in polar and arctic environments also makes them one of the foremost tools available for paleoclimatic reconstructions. They have been used for inferences of the former positions of the sea ice margin and oceanic fronts, as well as for inferring the distribution of water masses and to provide quantitative estimates of past sea surface temperatures (SSTs). These SST estimates are particularly being exploited for reconstructing the regional surface ocean conditions during the Holocene.
The transition from the last ice age to the present-day interglacial was interrupted by the Young... more The transition from the last ice age to the present-day interglacial was interrupted by the Younger Dryas (YD) cold period. While many studies exist on this climate event, only few include high-resolution marine records that span the YD. In order to better understand the interactions between ocean, atmosphere and ice sheet stability during the YD, more highresolution proxy records from the Arctic, located proximal to ice sheet outlet glaciers, are required. Here we present the first diatom-based high-resolution quantitative reconstruction of sea surface conditions from central-eastern Baffin Bay, covering the period 14.0–10.2kyr BP. Our record reveals warmer sea surface conditions and strong interactions between the ocean and the West Greenland ice margin during the YD. These warmer conditions were caused by increased Atlantic-sourced water inflow combined with amplified seasonality. Our results emphasize the importance of the ocean for ice sheet stability under the current changing climate.
A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studi... more A high-resolution marine sediment core NP16-Kro1-MCB from Krossfjorden, Western Svalbard is studied to investigate changes in sea surface conditions in the fjord during the last 60 years (1953–2014). The diatom-based reconstruction of August sea surface temperature (aSST) demonstrates a clear warming trend of 0.6 °C through the record. As inferred from Marginal Ice Zone (MIZ) diatoms, surface warming occurs in parallel with a decline in sea ice extent (SIE) during recent decades. Factor analysis identified variations in diatom assemblages representing different water masses, showing a dominance of Arctic water diatoms throughout the period and decadal variations in the sea ice assemblage during periods of peak sea ice extent. The strong dominance of Arctic water diatoms along with increasing aSST suggest prolonged open-water conditions and increased sea ice melting in the region throughout the observed period. The reconstructed ocean surface changes are in line with the background warming occurring over the Arctic region. A comparison with instrumental records from neighboring regions supports the quality of the reconstructions, including the average reconstructed aSST and the magnitude of the warming trend. We suggest that increased CO2 forcing together with ocean–atmospheric interaction have caused the increasing SST trend and decreasing sea ice presence in Krossfjorden rather than an increasing influence from Atlantic Water, which has amplified changes in many regions of Svalbard.
Sea surfaces temperatures (SSTs) are generated from a 1000-year-long sediment core from the easte... more Sea surfaces temperatures (SSTs) are generated from a 1000-year-long sediment core from the eastern flank of Reykjanes Ridge in the subpolar North Atlantic with a time resolution of 2-10 years. 54.3 cm long box core (Rapid 21-12B) and 370 cm long gravity core (RAPID 21-3K) were recovered from deep-sea sediments (2630 m water depth) during the RRS Charles Darwin cruise 159 in 2004. The box core is dated using the 210Pb method and it is continuously subsampled and investigated at 0.5 cm intervals for the last 230 years with a two years average time resolution. The gravity core is dated 14C AMS method and it is investigated continuously at 1.0 cm intervals with a ten years average resolution for the interval representing 230-1000 cal. years BP. August SSTs are reconstructed using marine planktonic diatom species with the Weighted Averages - Partial Least Squares (WA-PLS) method. Results achieved from the box core indicate August SST warming of c. 1 °C from 1773 AD to the present. The i...
ABSTRACT A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assem... more ABSTRACT A 2800-yr-long August sea surface temperature (aSST) record based on fossil diatom assemblages is generated from a marine sediment core Rapid 21-COM recovered in the Iceland Basin (northern subpolar North Atlantic). The record has a resolution of 2-10 years for interval 800-2004 AD representing the best resolved diatom SST reconstruction from the subpolar North Atlantic for this period, and 40 years for interval 800 BC-800 AD. The record is compared with the high-resolution (4-20 years) aSST record from core CR948/2011 from the Vøring Plateau, in the Norwegian Sea, to explore the variability of the aSST gradient between these areas during the late Holocene. The two aSST records show persistent opposite climate trends toward warming in the subpolar North Atlantic and cooling in the Norwegian Sea throughout the late Holocene. The wavelet analysis reveals an apparent tendency to coherent antiphased aSST variations between the sites for the shorter time scales too, implying a possible aSST seesaw between the northern subpolar North Atlantic and the Norwegian Sea to operate during the late Holocene. At the multicentennial scale of aSST variability of 600-900 years, the records are nearly in antiphase with warmer (colder) periods in the subpolar North Atlantic corresponding to the colder (warmer) periods in the Norwegian Sea. At the shorter time scale of 200-450 years the records display a nearly phase-locked behaviour with a tendency for the positive aSST anomalies in the Norwegian Sea to lead by ca. 30 years the negative aSST anomalies in the subpolar North Atlantic. This aSST seesaw might have had a strong effect, or be associated, with the two major climate anomalies in the northwest Europe during the past Millennium: Medieval Warm Period (MWP) and the Little Ice Age (LIA). During the MWP warming of the sea surface in the Norwegian Sea occurred in parallel with cooling in the northern subpolar North Atlantic, whereas the opposite pattern emerged during the LIA. Coupled changes in aSST between the northern subpolar North Atlantic and the Norwegian Sea may indicate common driving forces behind the observed variability. The emerging spatial pattern of aSST resembles the one predicted by some modelling studies and is associated with changes in the regimes of the North Atlantic overturning circulation (AMOC). The observed aSST seesaw between the subpolar North Atlantic and the Norwegian Sea could be a surface expression of the variability of the eastern and western branches of the AMOC with a possible amplification through atmospheric feedback.
ABSTRACT The Arctic region has undergone very rapid changes in the past 50 years. Climate models ... more ABSTRACT The Arctic region has undergone very rapid changes in the past 50 years. Climate models predict accelerating rates of change in the Arctic and long-term perspectives on natural climate variability are therefore needed to understand these changes and their further effects. We used marine fossil diatom assemblages from Baffin Bay to investigate August sea surface temperatures (aSSTs) and sea ice variability during the last two millennia. The Baffin Bay area is sensitive to changes in the climate system due to its location, where it is influenced by Atlantic and Arctic water masses. The top most 77 cm of a 600 cm long marine sediment core (GeoTü SL-170) was used for a high resolution study of quantitative SST and sea ice reconstructions based on fossil marine planktonic diatoms. A calibration dataset consisting of 155 surface samples from the North Atlantic and a new set of 24 surface samples from Baffin Bay with 52 diatom species was utilized to convert diatom counts to aSSTs using the weighted averaging partial least squares (WA-PLS) transfer function method. The sea ice reconstruction was based on a qualitative method for specific diatom assemblages and quantitative sea ice reconstructions for the May sea ice cover based on the Maximum likelihood (ML) transfer function method. The age model for the core is based on the 14C method. Our data shows a slight warming trend of the surface waters in Baffin Bay for the last ca. 2 kyr. The most dominating diatom species is Thalassiosira gravida spores, which represents typical "Baffin Current assemblage". The highest aSSTs occurred during the Medieval Warm Period (MWP), presumably due to the increased advection of warm Atlantic water from the West Greenland Current into Baffin Bay. After the MWP, the sediment was poor in diatoms during the Little Ice Age (LIA) suggesting that the study area was covered by sea ice also in the summertime.
August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated from a 2... more August Sea Surface Temperatures (aSSTs) based on fossil diatom assemblages are generated from a 230-year-long sediment core (Rapid 21-12B), from the southern limb of the Gardar Drift on the eastern flank of the Reykjanes Ridge in the subpolar North Atlantic. The reconstructed record has two years average resolution and represents the highest resolution diatom SST reconstruction from the subpolar North Atlantic. The results indicate a warming trend of ~0.5 °C of the surface waters in the Reykjanes Ridge area for the last 230 years. Superimposed on this warming trend there is a multidecadal to decadal aSST variability of up to 1 °C. The interval from the 1770s to the 1830s represents the coldest period, whereas ~1860-1880 represents the warmest period during the last 230 years. The last 25 years is characterized by a warming trend showing strong decadal aSST variability with several warm years, but also the coldest years since the 1820s. The time of these cold years in the mid-1970s, -1980s and -1990s correspond with the documented great salinity anomalies (GSA) in the North Atlantic suggesting increased fluxes of cold, low-salinity waters from the Arctic during the last decades. Results suggest that the wind driven variations in volume fluxes of the North Atlantic surface waters could be the major mechanism behind the observed aSST trends, because the aSST record and the August North Atlantic Oscillation (aNAO) index show similar multidecadal-scale variability indicating a close coupling between the oceanic and atmospheric patterns. Their relationship however is negative. On the long time scale, the aSST record shows an increasing (warming) trend, whereas the aNAO index shows a decreasing trend. On the multidecadal scale, smoothed records show warm aSST periods during the negative aNAO trends and cold aSSTs during the positive aNAO trends. This suggests that the strong westerlies during the positive aNAO phase drive the main part of the Atlantic surface water towards north. During the negative aNAO phase, the westerly winds over the Atlantic are weakened and could cause a remarkable increase in the westwards flowing warm Atlantic water across the Reykjanes Ridge area. The observed relationship between aSST and the aNAO, however, does not hold for the most recent period from the 1960s onwards, where aSSTs and the aNAO show co-phased variations at a decadal scale. This change in the observed SST/NAO system may be caused by the anthropogenic forcing and/or global warming.
The ‘Antrea Net Find’, found in 1913 in Korpilahti on the Karelian Isthmus, is one of the most im... more The ‘Antrea Net Find’, found in 1913 in Korpilahti on the Karelian Isthmus, is one of the most important archaeological discoveries in Finland. For a long time, it was the oldest dated net find in Europe. New sediment samples were taken from the assumed find spot in 1998. The original net material and the new sediment sequence around the find spot were re-investigated using modern physical and palaeoecological techniques. They included AMS radiocarbon dates from the net material and the sediment above the find, as well as lithostratigraphical and isotope analyses from the surrounding sediment sequence. Also the material of the net cord was investigated. The palaeoenvironment of the Korpilahti area around the time of the event was reconstructed using modern biostratigraphical diatom and pollen methods. The ‘Antrea Net Find’ was recovered from the uppermost part of silty clay gyttja. The AMS radiocarbon date of the net yielded an age of 9140±135 BP. The net cord has been made of willo...
A prominent characteristic of the reconstructed Northern Hemisphere temperature signal over the l... more A prominent characteristic of the reconstructed Northern Hemisphere temperature signal over the last millennium is the transition from the Medieval Climate Anomaly to the Little Ice Age (LIA). Here we report indications for a non-linear regime shift in the North Atlantic ocean circulation at the onset of the LIA. Specifically, we apply a novel statistical test based on horizontal visibility graphs to two ocean sediment August sea-surface temperature records from the Norwegian Sea and the central subpolar basin and find robust indications of time-irreversibility in both records during the LIA onset. Despite a basin-wide cooling trend, we report an anomalous warming in the central subpolar basin during the LIA that is reproduced in ensemble simulations with the climate model of intermediate complexity CLIMBER-3α as a result of a non-linear regime shift in the subpolar North Atlantic ocean circulation. The identified volcanically triggered non-linear transition in the model simulations...
ABSTRACT The classical Maximum Density data of 65 Torneträsk trees from years 441 to 1980 AD are ... more ABSTRACT The classical Maximum Density data of 65 Torneträsk trees from years 441 to 1980 AD are studied in millennial, centennial and volcanic scales. The millennial scale is analyzed applying a specific filtering method. In that scale, the climate is cool after 1200–1400 AD. This more or less steady period is suggested to be due to volcanic episodes, which reduced the northward heat transport in the North Atlantic. The century scale variation, on the other hand, is suggested to be due to internal oscillations in sea surface temperature (SST) and to be connected to variations in the Arctic sea ice. Specifically, these oscillations have caused an additional warming and cooling trend in Northern Fennoscandian temperatures before and after 1930's, respectively. Variations in the temperature estimates are explained by the results for different temporal scales. All of them show local impacts leading to differences when compared with hemispheric estimates. The long-term estimate of the temperature as derived from the present Torneträsk data is found to be biased. The source of that is unknown.
ABSTRACT Preservation of diatoms in sediments of the North Atlantic and Arctic Ocean through geol... more ABSTRACT Preservation of diatoms in sediments of the North Atlantic and Arctic Ocean through geological time has been highly variable. The North Atlantic Ocean and the Nordic Seas were a region of high productivity of biogenic silica until the onset of Northern Hemisphere glaciations during the late Miocene. Later, fluctuating Pleistocene climatic conditions had a major impact on diatom productivity in the high latitude North Atlantic. During interglacials high diatom productivity took place in the North Atlantic, whereas glacial stages are often barren of diatoms due to the expansion of sea ice cover. Diatom species show rapid evolution through time and therefore are an excellent biostratigraphic tool in this area. The high diversity of diatoms in polar and arctic environments also makes them one of the foremost tools available for paleoclimatic reconstructions. They have been used for inferences of the former positions of the sea ice margin and oceanic fronts, as well as for inferring the distribution of water masses and to provide quantitative estimates of past sea surface temperatures (SSTs). These SST estimates are particularly being exploited for reconstructing the regional surface ocean conditions during the Holocene.
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Papers by Arto Miettinen