Aerosol total mass concentration and optical depth during IPY 2007-2008 at Maitri and Larsemann Hills Station

The properties of background aerosols and their dependence on meteorological, geographical and human influence are examined using measured spectral aerosol optical depth (AOD), total mass concentration (Mt) and derived number size distribution (NSD) over two distinct coastal locations of Antarctica; Maitri (70°S, 12°E, 123 m m.s.l.) and Larsemann Hills (LH; 69°S, 77°E, 48 m m.s.l.) during southern hemispheric summer of 2007-2008 as a part of the 27th Indian Scientific Expedition to Antarctica (ISEA) during International Polar Year (IPY). Our investigations showed comparable values for the mean columnar AOD at 500 nm over Maitri (0.034±0.005) and LH (0.032±0.006) indicating good spatial homogeneity in the columnar aerosol properties over the coastal Antarctica. Estimation of Angstrom exponent a showed accumulation mode dominance at Maitri (alpha ~1.2±0.3) and coarse mode dominance at LH (0.7±0.2). On the other hand, mass concentration (M(T)) of ambient aerosols showed relatively high values (~8.25±2.87 µg/m**3) at Maitri in comparison to LH (6.03±1.33 µg/m**3).

Sea surface temperature estimation for MIS 16 of IODP Site 306-U1313

Hudson Strait (HS) Heinrich Events, ice-rafting events in the North Atlantic originating from the Laurentide ice sheet (LIS), are among the most dramatic examples of millennial-scale climate variability and have a large influence on global climate. However, it is debated as to whether the occurrence of HS Heinrich Events in the (eastern) North Atlantic in the geological record depends on greater ice discharge, or simply from the longer survival of icebergs in cold waters. Using sediments from Integrated Ocean Drilling Program (IODP) Site U1313 in the North Atlantic spanning the period between 960 and 320 ka, we show that sea surface temperatures (SSTs) did not control the first occurrence of HS Heinrich(-like) Events in the sedimentary record. Using mineralogy and organic geochemistry to determine the characteristics of ice-rafting debris (IRD), we detect the first HS Heinrich(-like) Event in our record around 643 ka (Marine Isotope Stage (MIS) 16), which is similar as previously reported for Site U1308. However, the accompanying high-resolution alkenone-based SST record demonstrates that the first HS Heinrich(-like) Event did not coincide with low SSTs. Thus, the HS Heinrich(-like) Events do indicate enhanced ice discharge from the LIS at the end of the Mid-Pleistocene Transition, not simply the survivability of icebergs due to cold conditions in the North Atlantic.

Sea surface temperature estimation of the South Tasman Rise

The Subtropical Front (STF) marking the northern boundary of the Southern Ocean has a steep gradient in sea surface temperature (SST) of approximately 4°C over 0.5° of latitude. Presently, in the region south of Tasmania, the STF lies nominally at 47°S in the summer and 45°S in the winter. We present here SST reconstructions in a latitudinal transect of cores across the South Tasman Rise, southeast of Australia, during the late Quaternary. SST reconstructions are based on two paleotemperature proxies, alkenones and faunal assemblages, which are used to assess past changes in SST in spring and summer. The north-south alignment in core locations allows reconstruction of movement of the STF over the last 100 ka. Surface water temperatures during the last glaciation in this region were ~4°C colder than today. Additional temperature changes greater in magnitude than 4°C seen in individual cores can be attributed to changes in the water mass overlying the core site caused by the movement of the front across that location. During the penultimate interglacial, SST was ~2°C warmer and the STF was largely positioned south of 47°S. Movement of the STF to the north occurred during cool climate periods such as the last marine isotope stages 3 and 4. In the last glaciation, the front was at its farthest north position, becoming pinned against the Tasmanian landmass. It moved south by 4° latitude to 47°S in summer during the deglaciation but remained north of 45°S in spring throughout the early deglaciation. After 11 ka B.P. inferred invigoration of the East Australia Current appears to have pushed the STF seasonally south of the East Tasman Plateau, until after 6 ka B.P. when it achieved its present configuration.

TEX86 values and temperature estimation for sediment trap samples

The newly introduced temperature proxy, the tetraether index of archaeal lipids with 86 carbon atoms (TEX86), is based on the number of cyclopentane moieties in the glycerol dialkyl glycerol tetraether (GDGT) lipids of marine Crenarchaeota. The composition of sedimentary GDGTs used for TEX86 paleothermometry is thought to reflect sea surface temperature (SST). However, marine Crenarchaeota occur ubiquitously in the world oceans over the entire depth range and not just in surface waters. We analyzed the GDGT distribution in settling particulate organic matter collected in sediment traps from the northeastern Pacific Ocean and the Arabian Sea to investigate the seasonal and spatial distribution of the fluxes of crenarchaeotal GDGTs and the origin of the TEX86 signal transported to the sediment. In both settings the TEX86 measured at all trap deployment depths reflects SST. In the Arabian Sea, analysis of an annual time series showed that the SST estimate based on TEX86 in the shallowest trap at 500 m followed the in situ SST with a 1 to 3 week time delay, likely caused by the relatively low settling speed of sinking particles. This revealed that the GDGT signal that reaches deeper water is derived from the upper water column rather than in situ production of GDGTs. The GDGT temperature signal in deeper traps at 1500 m and 3000 m did not show a seasonal cyclicity observed in the 500 m trap but rather reflected the annual mean SST. This is probably due to a homogenization of the TEX86 SST signal carried by particles as they ultimately reach the interior of the ocean. Our data confirm the use of TEX86 as a temperature proxy of surface ocean waters.

Temperature and CO2 estimation for the Middle Eocene section of ODP Hole 189-1172A

The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.