Description: Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias...

Description: Paleotemperature proxy data form the cornerstone of paleoclimate research and are integral to understanding the evolution of the Earth system across the Phanerozoic Eon. Here, we present PhanSST, a database containing over 150,000 data points from five proxy systems that can be used to estimate past sea surface temperature. The geochemical data have a near-global spatial distribution and temporally span most of the Phanerozoic. Each proxy value is associated with consistent and queryable metadata fields, including information about the location, age, and taxonomy of the organism from which the data derive. To promote transparency and reproducibility, we include all available published data, regardless of interpreted preservation state or vital effects. However, we also provide expert-assigned diagenetic assessments, ecological and environmental flags, and other proxy-specific fields, which facilitate informed and responsible reuse of the database. The data are quality control checked and the foraminiferal taxonomy has been updated. PhanSST will serve as a valuable resource to the paleoclimate community and has myriad applications, including evolutionary geochemical, diagenetic, and proxy calibration studies.

Description: Mumiyo deposits form in the vicinity of snow petrel (Pagodroma nivea) nesting sites and consist of fossil stomach oil (mumiyo), guano, and minerogenic material. Here we evaluate mumiyo deposits from the inland mountain ranges of central Dronning Maud Land as high-resolution archives for paleoenvironmental reconstructions in Antarctica. Investigation of internal structures and chemical composition shows that the lamination reflects progressive sedimentation, despite the irregular outer morphology of the deposits. Detailed radiocarbon analysis demonstrates that stratigraphies are intact: 14C ages become successively younger upwards in the deposits. Fatty acid and n-alcohol composition was determined on samples from eight mumiyo deposits. Dominance of low molecular weight compounds (C14 to C18) points to a dietary signal; however, the relatively low proportions of unsaturated compounds compared to fresh stomach oils indicates some postdepositional degradation. We found marine diatoms in the mumiyo, which potentially provide a proxy for sea ice conditions in the foraging habitat of the petrels. Age ranges of the investigated deposits suggest occupation of the analyzed sites by snow petrels from 17 ka to 〉58 ka. Changes in deposition rates point to higher occupation frequency in Petermann Range from 46 to 42 ka compared to the late marine isotope stage 3 and the Last Glacial Maximum.

Description: The West Antarctic Ice Sheet (WAIS) is one of the largest potential sources of future sea-level rise, with glaciers draining the WAIS thinning at an accelerating rate over the past 40 years. Due to complexities in calibrating palaeoceanographic proxies for the Southern Ocean, it remains difficult to assess whether similar changes have occurred earlier during the Holocene or whether there is underlying centennial- to millennial-scale forcing in oceanic variability. Archaeal lipid-based proxies, specifically glycerol dialkyl glycerol tetraether (GDGT; e.g. TEX86 and TEX), are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL)-GDGTs, representing (recently) living archaeal populations in suspended particulate matter (SPM) from the Amundsen Sea and the Scotia Sea. SPM samples from the Amundsen Sea were collected from up to four water column depths representing the surface waters through to Circumpolar Deep Water (CDW), whereas the Scotia Sea samples were collected along a transect encompassing the sub-Antarctic front through to the southern boundary of the Antarctic Circumpolar Current. IPL-GDGTs with low cyclic diversity were detected throughout the water column with high relative abundances of hydroxylated IPL-GDGTs identified in both the Amundsen and Scotia seas. Results from the Scotia Sea show shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean. Indicating that the physicochemical parameters of these water masses determine changes in IPL-GDGT distributions. The Amundsen Sea results identified GDGTs with hexose-phosphohexose head groups in the CDW, suggesting active GDGT synthesis at these depths. These results suggest that GDGTs synthesised at CDW depths may be a significant source of GDGTs exported to the sedimentary record and that temperature reconstructions based on TEX86 or TEX proxies may be significantly influenced by the warmer waters of the CDW.

Description: The Mid Pleistocene Transition (MPT) constitutes a fundamental shift in Earth's climate system from a 41 ka to a 100 ka periodicity in glacial oscillations. The exact timing and mechanism(s) that caused this change from a low- to high-amplitude glacial variability are still under debate and only recently Pena & Goldstein (2014) suggested that a disruption of the thermohaline circulation at about 900 ka BP and a subsequent change in ocean circulation might have acted as a trigger for the onset of 100 ka glacial-interglacial cycles. Most studies targeting the MPT are based on Atlantic sediment records whereas only few data sets are available from the North Pacific (see e.g. Clark et al., 2006 and McClymont et al., 2013 for reviews). IODP Expedition 341 distal deep-water site U1417 in the Gulf of Alaska (subpolar NE Pacific) now provided a continuous sediment record for reconstructing Miocene to Late Pleistocene changes in the sea surface conditions and how these relate to orbital and millennial scale climate variability. Here we present organic geochemical biomarker data covering the 1.5 Ma to 0.1 Ma time interval with special focus on the MPT. Alkenone, sterol, n-alkane and C25 highly branched isoprenoid data are used to reconstruct sea surface temperatures, primary productivity and terrigenous organic matter input (via sea ice, icebergs, meltwater discharge or aeolian transport). In addition, the diatom concentration and the species composition of the diatom assemblage deliver information on changes in palaeoproductivity and nutrient (silicate) availability. A major change in the environmental setting between 1.2 and 0.8 Ma is recorded by the biomarkers. This shift seems to be associated with a significant cooling of the surface waters in the Gulf of Alaska. Matching this shift, a significant change in the main components of the diatom community occurred between 1.2 and 0.8 Ma. References Clark, P.U., Archer, D., Pollard, D., Blum, J.D., Rial, J.A., Brovkin, V., Mix, A.C., Pisias, N.G., Roy, M., 2006. Quaternary Science Reviews, 25, (23–24), 3150-3184. McClymont, E.L., Sosdian, S.M., Rosell-Melé, A., Rosenthal, Y., 2013. Earth-Science Reviews, 123, 173-193. Pena, L.D. and Goldstein, S.L., 2014. Science, 345, 318-322.

Description: A remarkable sedimentary record that extends from the Miocene to the late Pleistocene/Holocene has been drilled during IODP Expedition 341 (May - July 2013) in the Gulf of Alaska. The recovery and examination of sediments along a transect of five drill sites (U1417 - U1421) from the deep ocean towards the continental slope and offshore the St. Elias Mountains enables the reconstruction of the palaeoceanographic and environmental development in the NE Pacific during a period of significant global cooling and directly addresses the overall research objectives of the IODP programme. The knowledge about palaeo sea surface conditions and their relation to climate changes in the subpolar NE Pacific is relatively scarce and mainly confined to the past 17 ka BP (Barron et al., 2009; Davies et al., 2011; Addison et al., 2012). Biomarker based reconstructions of the sea surface conditions (i.e. sea surface temperature(SST), sea ice coverage, marine primary productivity) that characterised the subpolar NE Pacific during critical time intervals of Plio- and Pleistocene climate change may provide new information on oceanic and atmospheric feedback mechanisms and further enable the identification of teleconnections between the palaeoceanographic evolution in the North Pacific and the North Atlantic. Here we present preliminary biomarker data obtained from sediments from the distal deepwater site U1417 and the proximal site U1419 located at the Gulf of Alaska continental slope. Variability in the distribution and abundance of short- and long-chain n-alkanes, sterols, and C25-highly branched isoprenoids (HBIs) is interpreted to reflect changes in the environmental setting. These data provide insight in marine primary productivity changes(in response to cooling and warming intervals) and the variable input of terrigenous organic matter via meltwater and/or iceberg discharge events. The C25-HBI diene/triene ratio - hitherto used as a sea ice proxy in the Southern Ocean (Etourneau et al., 2013) - is applied to gain information about the variability in polar water/sea ice extent in the study area. Previously, Rowland et al. (2001) documented that not only the degree of unsaturation in C25-HBIs but also the E- to Z-isomerisation in the C25-HBI trienes increases with increasing water temperature. Based on this observation we suggest that the ratio of the Z-isomer to the E-isomer in the trienes might reflect SST changes and could be used as an additional SST proxy. The applicability of this approach, however, needs further evaluation (e.g. through comparisons with alkenone SST data obtained from Expedition 341 sediments).

Description: The exact timing and mechanism(s) that caused a change from a low- to high-amplitude glacial variability during the Mid Pleistocene Transition (MPT) - a fundamental shift in Earth’s climate system - are still under debate. Most studies targeting the MPT are based on Atlantic sediment records whereas only few data sets are available from the North Pacific (see Clark et al., 2006 and McClymont et al., 2013 for reviews). IODP Expedition 341 distal deep-water site U1417 in the Gulf of Alaska (subpolar NE Pacific) now provides a continuous sediment record for reconstructing Miocene to Late Pleistocene changes in the sea surface conditions and their linkage to ice-sheet fluctuations on land. Here we present organic geochemical biomarker data covering the 1.5 Ma to 0.1 Ma time interval with special focus on the MPT. Alkenone, sterol, n-alkane and C25 highly branched isoprenoid data are used to reconstruct sea surface temperatures, primary productivity and terrigenous organic matter input (via sea ice, icebergs, meltwater discharge or aeolian transport). In addition, the diatom concentration and the species composition of the diatom assemblage allow estimates of palaeoproductivity and nutrient (silicate) availability. Information about ice-sheet dynamics (and associated iceberg calving) and sea ice coverage is derived from ice rafted detritus (IRD) data. A key observation is a significant SST cooling at about 1 Ma, which is in close agreement with other Northern Hemisphere SST records. We further observe that short-term maxima in the diatom abundances coincide with peak deposition of terrigenous biomarkers and IRD minima. References Clark, P.U. et al. 2006. Quaternary Science Reviews, 25 (23–24): 3150-3184. McClymont, E.L. et al. 2013. Earth-Science Reviews 123: 173-193.