Sea surface temperature reconstruction from biomarker in sediments off Portugal

High resolution reconstructions of sea surface temperature (Uk'37-SST), coccolithophore associations and continental input (total organic carbon, higher plant n-alkanes, n-alkan-1-ols) in core D13882 from the shallow Tagus mud patch are compared to SST records from deep-sea core MD03-2699 and other western Iberian Margin cores. Results reveal millennial-scale climate variability over the last deglaciation, in particular during the LGIT. In the Iberian margin, Heinrich event 1 (H1) and the Younger Dryas (YD) represent two extreme episodes of cold sea surface condition separated by a marine warm phase that coincides with the Bølling-Allerød interval (B-A) on the neighboring continent. Following the YD event, an abrupt sea surface warming marks the beginning of the Holocene in this region. SSTs recorded in core D13882 changed, however, faster than those at deep-sea site MD03-2699 and at the other available palaeoclimate sequences from the region. While the SST values from most deep-sea cores reflect the latitudinal gradient detected in the Iberian Peninsula atmospheric temperature proxies during H1 and the B-A, the Tagus mud patch (core D13882) experienced colder SSTs during both events. This is most certainly related to a supplementary input of cold freshwater from the continent to the Tagus mud patch, a hypothesis supported by the high contents of terrigenous biomarkers and total organic carbon as well as by the dominance of tetra-unsaturated alkenone (C37:4) observed at this site. The comparison of all western Iberia SST records suggests that the SST increase that characterizes the B-A event in this region started 1000 yr before meltwater pulse 1A (mwp-1A) and reached its maximum values during or slightly after this episode of substantial sea-level rise. In contrast, during the YD/ Holocene transition, the sharp SST rise in the Tagus mud patch is synchronous with meltwater pulse IB. The decrease of continental input to the mud patch conflrms a sea level rise in the region. Thus, the synchronism between the maximum warming in the mid-latitudes off the western Iberian margin, the adjacent landmasses and Greenland indicates that mwp-lB and the associated sea-level rise probably initiated in the Northern Hemisphere rather than in the South.

Sea surface temperature reconstruction for ODP Hole 178-1098B

The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica (Cook et al., 2005, doi:10.1126/science.1104235; Stammerjohn et al., 2008, doi:10.1016/j.dsr2.2008.04.026) highlight the impact of recent atmospheric (Steig et al., 2009, doi:10.1038/nature07669) and oceanic warming (Gille, 2002, doi:10.1126/science.1065863) on the cryosphere. Observations (Cook et al., 2005, doi:10.1126/science.1104235; Stammerjohn et al., 2008, doi:10.1016/j.dsr2.2008.04.026) and models (Pollard and DeConto, 2009, doi:10.1038/nature07809) suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000?years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX86 sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations (Huybers and Denton, 2008, doi:10.1038/ngeo311). On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability (Mayewski et al., 2004, doi:10.1016/j.yqres.2004.07.001). Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions (Moreno et al., 2010, doi:10.1130/G30962.1) and El Niño/Southern Oscillation variability (Conroy et al., 2008, doi:10.1016/j.quascirev.2008.02.015) indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula (Yuan et al., 2004, doi:10.1017/S0954102004002238) strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling (Moreno et al., 2010, doi:10.1130/G30962.1; Anderson et al., 2009, doi:10.1126/science.1167441).

Sea surface temperature variations in the western Mediterranean Sea

A high-resolution sea surface temperature (SST) reconstruction of the western Mediterranean was accomplished using two independent, algae-based molecular organic proxies, i.e. the UK'37 index based on long-chain unsaturated ketones and the novel long-chain diol index (LDI) based on the relative abundances of C28 and C30 1,13- and 1,15-diols. Two marine records, from the western and eastern Alboran Sea basin, spanning the last 14 and 20 kyr, respectively, were studied. Results from the surface sediments suggest that the two proxies presently reflect seasons with similar SST, or simply annual mean SST. Both proxy records reveal the transition from the Last Glacial Maximum to the Holocene in the eastern Alboran Sea with an SST increase of ca. 7 °C for UK'37 and 9 °C for LDI. Minimum SSTs (10-12 °C) are reached at the end of the Last Glacial Maximum and during the last Heinrich event with a subsequent rapid SST increase in LDI-SST towards the beginning of the Bölling period (20 °C), while UK'37-SST remains constantly low (~12 °C). The Bölling-Alleröd is characterized by a rapid increase and subsequent decrease in UK'37-SST, while the LDI-SST decrease continuously. Short-term fluctuations in UK'37-SST are probably related to availability of nutrients and seasonal changes. The Younger Dryas is recorded as a short cold interval followed by progressively warmer temperatures. During the Holocene, the general lower UK'37-derived temperature values in the eastern Alboran (by ca. 1.5-2 °C) suggest a southeastward cold water migration by the western Alboran gyre and divergence in the haptophyte blooming season between both basins.

Age determination and sea surface temperature reconstruction from marine and lake records, Iberian Peninsula

Selected multi-proxy and accurately dated marine and terrestrial records covering the past 2000 years in the Iberian Peninsula (IP) facilitated a comprehensive regional paleoclimate reconstruction for the Medieval Climate Anomaly (MCA: 900-1300 AD). The sequences enabled an integrated approach to land-sea comparisons and, despite local differences and some minor chronological inconsistencies, presented clear evidence that the MCA was a dry period in the Mediterranean IP. It was a period characterized by decreased lake levels, more xerophytic and heliophytic vegetation, a low frequency of floods, major Saharan eolian fluxes, and less fluvial input to marine basins. In contrast, reconstruction based on sequences from the Atlantic Ocean side of the peninsula indicated increased humidity. The data highlight the unique characteristics of the MCA relative to earlier (the Dark Ages, DA: ca. 500-900 years AD) and subsequent (the Little Ice Age, LIA: 1300-1850 years AD) colder periods. The reconstruction supports the hypothesis of Trouet et al. (2009, doi:10.1126/science.1166349), that a persistent positive mode of the North Atlantic Oscillation (NAO) dominated the MCA.