HOLOCENE CLIMATE VARIABILITY AND ECOSYSTEM CHANGES IN COASTAL EAST AND MARITIME ANTARCTICA “HOLANT” (SD/CA/01)

The Earth’s climate undergoes significant changes, which are not yet fully understood. Recent climate models revealed that the Southern Hemisphere and Antarctica in particular could have been of significant influence in past abrupt and large climate change events. Although the Holocene has not experienced climate changes of the same magnitude as during the major Quaternary glaciations, it has been marked by many, often rapid, global temperature and precipitation anomalies. In order to understand how Antarctic temperature variation can impact other regions on Earth and to test competing models concerning the causes, the spatial interrelationships and characteristics of these climate anomalies, it is necessary to learn from the record of past natural climate variability. The IGBP has recognised this need by starting a global coordination of paleoclimate studies along 3 North-South transects (i.e., the PAGES-project PEP 1, 2 and 3 traverses) in order to build a strong high-resolution network of paleoclimate studies. The goal of the PEPs is to reconstruct paleoenvironments and paleoclimate along three terrestrial transects using a multi-proxy data and modeling approach. However, these transects currently end at Southern latitudes of 52S, and are not yet fully interlinked with the ice cores from the Antarctic plateau.
HOLANT explicitly extended the PEP 1 transect towards Sub- and coastal Maritime Antarctica and contribute to the PEP2 and 3 transects by establishing and comparing a series of high-resolution records of Holocene climate variability in coastal Antarctica based on biological and sedimentological proxies in (coastal) lake sediments. Since 2006, PAGES science has been redefined; within this new science structure, HOLANT will contribute to all 4 PAGES scientific foci (www.pages.unibe.ch) through three specific research questions: (i) What are the timing, duration and magnitude of Holocene climate anomalies in coastal areas in maritime, east and Sub-Antarctic regions and how are these anomalies related to climatic events recorded in inland locations (ice cores) ? (ii) How did Holocene climate changes affect regional ice sheet/glacier dynamics ? and (iii) How did Holocene climate changes affect the diversity of primary producers in Antarctic lakes ? The main findings of HOLANT can be summarized as follows:
(1) Past Climate variability in South Georgia
The sediment record from Fan Lake (Annenkov Island, South Georgia) extends back to c. 8 ka, which postdates a period of marked early Holocene warmth identified in Antarctic ice cores, and marine and lacustrine sediment records.High-ultra high resolution (mm-sub mm) variability in both gamma density and major element geochemistry (measured using ITRAX-XRF down to 200 microns) suggest the lake system possibly responds to annual/multi-annual and/or decadal/multi-decadal variations in climate in this part of the South Atlantic in the last 4 ka. In combination with newly retrieved sediment cores (field season 2008-2009) within the BAS CACHE-PEP program, this will allow us to reconstruct past climate variability on a high temporal resolution in a region which lacks such data.
(2) Long-term Westerly dynamics during the Holocene on Kerguelen Archipelago
Within the four seismic-stratigraphic units identified in the sedimentary infill of Lac d’Armor (Kerguelen Archipelago), the upper unit is characterised by the presence of distinct mounded depocentres, which closely resemble drift deposits and thus suggest the influence of strong bottom currents. Given the specific setting, such bottom currents are likely wind-driven. We interpret the occurrence of these drift deposits as an indication of a strengthening of the influence of the westerlies during this period. Future long cores may provide confirmation of this hypothesis and may allow dating this important environmental change on Kerguelen Archipelago.
(3) Paleoprecipitation and paleoclimate in Kerguelen during the Late Holocene
Up to present, very little paleoclimatic, and even less paleohydrological, records exist of the Holocene in the oceanic realm of the southern hemisphere. In the Kerguelen Archipelago, the sedimentary records from Lac d’Armor are characterized by a main transition toward lower detrital input –and hence very likely to lower precipitation– since 1400 AD. Despite a weaker chronological control compared to ice core records, our Sibio signal presents a significant correlation with the Naxs signal from Siple Dome. This implies that to some extent, high-frequency variability of the westerlies impacted the climate on Kerguelen Archipelago through an anti-correlation between strength of the westerlies and precipitation over the last millennium. It remains unclear if the high terrigenous input in Lac Armor represents the local expression of the Little Ice Age (LIA) in the Kerguelen Archipelago, or if a local LIA expression is actually out of phase with the northern hemisphere.
(4) Transfer functions for paleoclimate reconstructions
Transfer functions were developed to quantitatively reconstruct past changes in the nutrient concentration of Maritime Antarctic lakes. Together with the fossil pigment concentration, this will allow us to infer temperature dependent changes in lake primary productivity. The transfer function for the Lützow Holm Bay region extends an existing model and will allow us to reconstruct temperature dependent changes in salinity in a wide sector of East Antarctica between 10 and 110°E. Both models have good to excellent predictive power and the error statistics are sufficiently low.