Sea surface temperture reconstruction for ODP Site 189-1172

Relative to the present day, meridional temperature gradients in the Early Eocene age (~56-53 Myr ago) were unusually low, with slightly warmer equatorial regions (Pearson et al., 2007, doi:10.1130/G23175A.1 ) but with much warmer subtropical Arctic (Sluijs et al., 2008, doi:10.1029/2007PA001495) and mid-latitude (Sluijs et al., 2007, doi:10.1038/nature06400) climates. By the end of the Eocene epoch (~34 Myr ago), the first major Antarctic ice sheets had appeared (Zachos et al., 1992, doi:10.1130/0091-7613(1992)020<0569:EOISEO>2.3.CO;2; Barker et al., 2007, doi:10.1016/j.dsr2.2007.07.027), suggesting that major cooling had taken place. Yet the global transition into this icehouse climate remains poorly constrained, as only a few temperature records are available portraying the Cenozoic climatic evolution of the high southern latitudes. Here we present a uniquely continuous and chronostratigraphically well-calibrated TEX86 record of sea surface temperature (SST) from an ocean sediment core in the East Tasman Plateau (palaeolatitude ~65° S). We show that southwest Pacific SSTs rose above present-day tropical values (to ~34° C) during the Early Eocene age (~53 Myr ago) and had gradually decreased to about 21° C by the early Late Eocene age (~36 Myr ago). Our results imply that there was almost no latitudinal SST gradient between subequatorial and subpolar regions during the Early Eocene age (55-50 Myr ago). Thereafter, the latitudinal gradient markedly increased. In theory, if Eocene cooling was largely driven by a decrease in atmospheric greenhouse gas concentration Zachos et al. (2008, doi:10.1038/nature06588), additional processes are required to explain the relative stability of tropical SSTs given that there was more significant cooling at higher latitudes.

Clay mineral and stratigraphic record of two sediment cores from the Aegean Sea

Different source areas, oceanography and climate regimes influenced the clay mineral assemblages and grain size distribution of two sediment cores from the North and South Aegean Sea during the last glacial and the Holocene. In the North Aegean Sea, clay mineral composition is mainly controlled by sea level evolution, melting of southeastern European glaciers, and establishment of the connection between the Black Sea and Aegean Sea. The long-term development of clay mineral assemblages in the South Aegean Sea reflects changes in the Nile discharge and African dust input. At this site, the establishment of pluvial conditions in the Nile catchment during the early to middle Holocene resulted in a substantial rise in smectite/illite ratios. In the late Holocene, stepwise aridification of the southern borderlands caused an increase in windblown sediment material and a decrease in Nile suspended material. The clay mineral records exhibit periodic millennial-scale fluctuations. In the North Aegean Sea, the changes are centred at a period of 1.3-1.8 ka and can be attributed to short-term climate and weathering changes in the northern borderlands. The changes in the South Aegean Sea are centred at periods of 3.2-4.3, 1.9-2.4 and 1.3-1.7 ka reflecting short-term changes in wind strength and Northeast African hydrology.

Late Pliocene age models of Agulhas Plateau sediment cores

An ensemble of new, high-resolution records of surface ocean hydrography from the Indian-Atlantic oceanic gateway, south of Africa, demonstrates recurrent and high-amplitude salinity oscillations in the Agulhas Leakage area during the penultimate glacial-interglacial cycle. A series of millennial-scale salinification events, indicating strengthened salt leakage into the South Atlantic, appear to correlate with abrupt changes in the North Atlantic climate and Atlantic Meridional Overturning Circulation (AMOC). This interhemispheric coupling, which plausibly involved changes in the Hadley Cell and midlatitude westerlies that impacted the interocean transport at the tip of Africa, suggests that the Agulhas Leakage acted as a source of negative buoyancy for the perturbed AMOC, possibly aiding its return to full strength. Our finding points to the Indian-to-Atlantic salt transport as a potentially important modulator of the AMOC during the abrupt climate changes of the Late Pleistocene.

Multicentennial resolution proxy records from splicings of MD96-2080 and MD02-2594, Agulhas Bank Splice (ABS)

[1] Planktonic d18O and Mg/Ca-derived sea surface temperature (SST) records from the Agulhas Corridor off South Africa display a progressive increase of SST during glacial periods of the last three climatic cycles. The SST increases of up to 4°C coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites. Mg/Ca-derived SST maximizes during glacial maxima and glacial Terminations to values about 2.5°C above full-interglacial SST. The paired planktonic d18O and Mg/Ca-derived SST records yield glacial seawater d18O anomalies of up to 0.8 per mill, indicating measurably higher surface salinities during these periods. The SST pattern along our record is markedly different from a UK'37-derived SST record at a nearby core location in the Agulhas Corridor that displays SST maxima only during glacial Terminations. Possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of SST contrasts during glacials in association with seasonal changes of Agulhas water transports and lateral shifts of the Agulhas retroflection. The different SST reconstructions derived from UK'37 and Mg/Ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the Agulhas Current and interocean salt leakage is not as straightforward as previously suggested.

Deforesting Europe: pollen-inferred Holocene land cover change using the 'pseudobiomization' approach

Maps of continental-scale land cover are utilized by a range of diverse users but whilst a range of products exist that describe present and recent land cover in Europe, there are currently no datasets that describe past variations over long time-scales. User groups with an interest in past land cover include the climate modelling community, socio-ecological historians and earth system scientists. Europe is one of the continents with the longest histories of land conversion from forest to farmland, thus understanding land cover change in this area is globally significant. This study applies the pseudobiomization method (PBM) to 982 pollen records from across Europe, taken from the European Pollen Database (EPD) to produce a first synthesis of pan-European land cover change for the period 9000 BP to present, in contiguous 200 year time intervals. The PBM transforms pollen proportions from each site to one of eight land cover classes (LCCs) that are directly comparable to the CORINE land cover classification. The proportion of LCCs represented in each time window provides a spatially aggregated record of land cover change for temperate and northern Europe, and for a series of case study regions (western France, the western Alps, and the Czech Republic and Slovakia). At the European scale, the impact of Neolithic food producing economies appear to be detectable from 6000 BP through reduction in broad-leaf forests resulting from human land use activities such as forest clearance. Total forest cover at a pan-European scale moved outside the range of previous background variability from 4000 BP onwards. From 2200 BP land cover change intensified, and the broad pattern of land cover for preindustrial Europe was established by 1000 BP. Recognizing the timing of anthropogenic land cover change in Europe will further the understanding of land cover-climate interactions, and the origins of the modern cultural landscape.