• Energy Research

Recent modeling suggests that changes in Southern Ocean sea‐ice extent potentially regulated the exchange of CO2release between the ocean and atmosphere during glacials. Unfortunately, a lack of high‐resolution sea‐ice records from the Southern Ocean has prevented detailed testing of these model‐based hypotheses with field data. Here we present high‐resolution records of Southern Ocean sea‐ice, for the period 35–15 cal ka BP, derived from diatom assemblages measured in three glacial sediment cores forming an ∼8° transect across the Scotia Sea, southwest Atlantic. Chronological control was achieved through a novel combination of diatom abundance stratigraphy, relative geomagnetic paleointensity data, and down‐core magnetic susceptibility and ice core dust correlation. Results showed that the winter sea‐ice edge reached its maximum northward extent of ∼53°S, at least 3° north of its modern limit, between ∼25 and ∼23.5 cal ka BP, predating the Last Glacial Maximum (LGM). Maximum northward expansion of the summer sea‐ice edge also pre‐dated the LGM, advancing to at least 61°S, and possibly as far north as 55°S between ∼31 and ∼23.5 cal ka BP, a ∼12° advance from its modern position. A clear shift in the seasonal sea‐ice zone is evident following summer sea‐ice edge retreat at ∼23.5 cal ka BP, potentially related to austral insolation forcing. This resulted in an expanded seasonal sea‐ice zone between ∼22.5 cal ka BP and deglaciation. Our field data confirm that Southern Ocean sea‐ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre‐formed nutrients. Our data indicates that Southern Ocean sea‐ice was most effective as a physical barrier between ∼31 and ∼23.5 cal ka BP and as a mechanism capable of reducing vertical mixing between ∼22.5 cal ka BP and deglaciation. However, poor correlations with atmospheric CO2 variability recorded in ice cores, particularly the lack of a CO2response during a rapid sea‐ice meltback event, recorded at our study sites at the same time as Antarctic Isotopic Maximum 2, suggest that Southern Ocean sea‐ice in the Scotia Sea did not play a controlling role in atmospheric CO2 variation during the glacial.

Recent modeling suggests that changes in Southern Ocean sea‐ice extent potentially regulated the exchange of CO2release between the ocean and atmosphere during glacials. Unfortunately, a lack of high‐resolution sea‐ice records from the Southern Ocean has prevented detailed testing of these model‐based hypotheses with field data. Here we present high‐resolution records of Southern Ocean sea‐ice, for the period 35–15 cal ka BP, derived from diatom assemblages measured in three glacial sediment cores forming an ∼8° transect across the Scotia Sea, southwest Atlantic. Chronological control was achieved through a novel combination of diatom abundance stratigraphy, relative geomagnetic paleointensity data, and down‐core magnetic susceptibility and ice core dust correlation. Results showed that the winter sea‐ice edge reached its maximum northward extent of ∼53°S, at least 3° north of its modern limit, between ∼25 and ∼23.5 cal ka BP, predating the Last Glacial Maximum (LGM). Maximum northward expansion of the summer sea‐ice edge also pre‐dated the LGM, advancing to at least 61°S, and possibly as far north as 55°S between ∼31 and ∼23.5 cal ka BP, a ∼12° advance from its modern position. A clear shift in the seasonal sea‐ice zone is evident following summer sea‐ice edge retreat at ∼23.5 cal ka BP, potentially related to austral insolation forcing. This resulted in an expanded seasonal sea‐ice zone between ∼22.5 cal ka BP and deglaciation. Our field data confirm that Southern Ocean sea‐ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre‐formed nutrients. Our data indicates that Southern Ocean sea‐ice was most effective as a physical barrier between ∼31 and ∼23.5 cal ka BP and as a mechanism capable of reducing vertical mixing between ∼22.5 cal ka BP and deglaciation. However, poor correlations with atmospheric CO2 variability recorded in ice cores, particularly the lack of a CO2response during a rapid sea‐ice meltback event, recorded at our study sites at the same time as Antarctic Isotopic Maximum 2, suggest that Southern Ocean sea‐ice in the Scotia Sea did not play a controlling role in atmospheric CO2 variation during the glacial.

Annual temperatures on the Antarctic Peninsula, one of the most rapidly warming regions on Earth, have risen by up to 0.56°C per decade since the 1950s. Terrestrial and marine organisms have shown changes in populations and distributions over this time, suggesting that the ecology of the Antarctic Peninsula is changing rapidly. However, these biological records are shorter in length than the meteorological data, and observed population changes cannot be securely linked to longer-term trends apparent in paleoclimate data. We developed a unique time series of past moss growth and soil microbial activity from a 150-year-old moss bank at the southern limit of significant plant growth based on accumulation rates, cellulose δ(13)C, and fossil testate amoebae. We show that growth rates and microbial productivity have risen rapidly since the 1960s, consistent with temperature changes, although recently they may have stalled. The recent increase in terrestrial plant growth rates and soil microbial activity are unprecedented in the last 150 years and are consistent with climate change. Future changes in terrestrial biota are likely to track projected temperature increases closely and will fundamentally change the ecology and appearance of the Antarctic Peninsula.

Annual temperatures on the Antarctic Peninsula, one of the most rapidly warming regions on Earth, have risen by up to 0.56°C per decade since the 1950s. Terrestrial and marine organisms have shown changes in populations and distributions over this time, suggesting that the ecology of the Antarctic Peninsula is changing rapidly. However, these biological records are shorter in length than the meteorological data, and observed population changes cannot be securely linked to longer-term trends apparent in paleoclimate data. We developed a unique time series of past moss growth and soil microbial activity from a 150-year-old moss bank at the southern limit of significant plant growth based on accumulation rates, cellulose δ(13)C, and fossil testate amoebae. We show that growth rates and microbial productivity have risen rapidly since the 1960s, consistent with temperature changes, although recently they may have stalled. The recent increase in terrestrial plant growth rates and soil microbial activity are unprecedented in the last 150 years and are consistent with climate change. Future changes in terrestrial biota are likely to track projected temperature increases closely and will fundamentally change the ecology and appearance of the Antarctic Peninsula.

We review the post-glacial climate variability along the East Antarctic coastline using terrestrial and shallow marine geological records and compare these reconstructions with data from elsewhere. Nearly all East Antarctic records show a near-synchronous Early Holocene climate optimum (11.5-9 ka BP), coinciding with the deglaciation of currently ice-free regions and the optimum recorded in Antarctic ice and marine sediment cores. Shallow marine and coastal terrestrial climate anomalies appear to be out of phase after the Early Holocene warm period, and show complex regional patterns, but an overall trend of cooling in the terrestrial records. A Mid to Late Holocene warm period is present in many East Antarctic lake and shallow coastal marine records. Although there are some differences in the regional timing of this warm period, it typically occurs somewhere between 4.7 and 1 ka BP, which overlaps with a similar optimum found in Antarctic Peninsula terrestrial records. The differences in the timing of these sometimes abrupt warm events in different records and regions points to a number of mechanisms that we have yet to identify. Nearly all records show a neoglacial cooling from 2 ka BP onwards. There is no evidence along the East Antarctic coastline for an equivalent to the Northern Hemisphere Medieval Warm Period and there is only weak circumstantial evidence in a few places for a cool event crudely equivalent in time to the Northern Hemisphere's Little Ice Age. There is a need for well-dated, high resolution climate records in coastal East Antarctica and particularly in Terre Adélie, Dronning Maud Land and Enderby Land to fully understand the regional climate anomalies, the disparity between marine and terrestrial records, and to determine the significance of the heterogeneous temperature trends being measured in the Antarctic today. © 2010 Elsevier B.V.