The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. The Pacific sector of the ACC clearly lacks information on its Cenozoic paleoceanography from deep-sea drilling records. To advance our understanding of Miocene to Holocene atmosphere- ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, we aim to investigate surface ocean changes in the northern ACC system. We will provide a unique reference record of sea surface temperature (SST) changes at orbital to suborbital time-scales to (i) evaluate the development of the large scale SST gradients across the subantarctic South Pacific and meridionally along the eastern South Pacific into the tropics, to (ii) capture long-term changes in the ACC water transported through the Drake Passage and entering the Atlantic meridional overturning circulation, and to (iii) assess the links between the thermal history of the eastern South Pacific and the dynamics of the West Antarctic and Patagonian Ice sheets. Our SST reconstructions will be based on biomarker analyses on samples from IODP Site U1543 located at ~3850 m water depth west of southern Chile at the entrance of the Drake Passage. Pleistocene SST records showed that paleo-SSTs based on UK37 paleothermometry is a highly reliable method in this subantarctic region of the Pacific. The ship- board age model for this site suggests continuous sedimentation (~5 cm/ka) throughout the past ~8 Ma. Precise age control is provided through a combination of numerous biostratigraphic markers, an exceptional paleomagnetic record, and a promising stratigraphic tuning of physical property and XRF data back to the uppermost part of the Miocene, which is to our knowledge unprecedented for the Southern Ocean. Except for subantarctic Atlantic ODP Site 1090 and ODP Sites off New Zealand (e.g. Sites 593 and 594), no continuous SST record presently extends beyond 3.5 Ma and the long-term thermal history of the Pacific as the largest Southern Ocean sector is only poorly constrained. We will document surface ocean conditions during the relatively stable warm periods of the late Miocene and Pliocene with atmospheric CO2 similar to today and will analyze how orbital-scale SST variations in the subantarctic ACC responded to different modes of orbital forcing under warmer- than-present climates. Moreover, we will learn how SSTs in the eastern South Pacific relate to the general Plio-Pleistocene cooling trend and the onset of major northern hemisphere glaciation and how orbital-scale variability changed across major Pleistocene climate transitions such as the Mid-Pleistocene Revolution. Finally, we will identify the relevance of eastern South Pacific SSTs for the development and the dynamics of the West Antarctic and Patagonian Ice Sheets.

Current climate change is a major threat to marine biodiversity with severe effects on marine ecosystem function and stability. Phytoplankton, at the base of marine food webs, already start showing shifts in species composition and abundance as a consequence. Yet it is unclear how such changes occurred in the past and likely continue in the future. PHYTOARK looks into the Holocene history of the Baltic Sea to estimate patterns of phytoplankton biodiversity in the past and to assess its ecosystem function under global change. The project will address the questions: 1. How did primary producer communities react to rising temperatures and changing salinities during Holocene warm periods? 2. Did populations of key species change over time? 3. Does climate change and human impact accelerate these changes? 4. How will phytoplankton of the future function? We answer these questions through an integrative approach that combines the newest advances in environmental DNA time series, paleo-genomics, molecular organic proxies, resurrection ecology and ecological modelling. We will analyse dated sediment cores capturing ~8000 years of Baltic history to reconstruct phytoplankton composition and function based on eDNA and trait information, document evolutionary adaptation and trait changes of populations on resurrected individuals and eDNA signatures, project future phytoplankton biodiversity and function in models and define reference status variability to aid environmental assessment efforts. PHYTOARK places eco-evolutionary changes of phytoplankton into a multi-millennial context to understand, predict and monitor the consequences of global change in marine ecosystems. Connecting excellence in biodiversity, climate change, paleo-ecology and marine system science, the network will generate a new association of Leibniz Institutions and Universities that can significantly advance an integrative understanding of human impact on marine biodiversity and ecosystem function.

The national BaltRap network, based at the Leibniz Institute for Baltic Sea Research Warnemünde (IOW), is a project funded in the frame of the Leibniz Competition 2017. BaltRap aims to comprehensively understand the impact of rapid climate change in the southern Baltic Sea region during the Holocene by integrating high-resolution marine (sediments) and terrestrial (lake sediments and tree rings) proxy archives. The network is based on a very close interdisciplinary collaboration between scientists from IOW, the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), the University of Greifswald (EMAU), and the Helmholtz-Zentrum Potsdam Deutsches GeoForschungsZentrum (GFZ). BaltRap represents an adequate platform to provide a better understanding of the variable sensitivities and response times of the coupled marine-terrestrial system to the combined effects of long term and rapid climate change, and human impact.

Recently developed organic proxies (TEX86, MBT/CBT, OH-GDGT1318/cren) based on glycerol dialkyl glycerol tetraether (GDGT) membrane lipids from ammonia-oxidizing Archaea (Thaumarchaeota) and Bacteria provide a unique tool to reconstruct the temperature history of the Baltic Sea region. However, factors, such as the diversity of GDGTs producers, their distribution in the water column, seasonality and water oxygen concentration may affect the interpretation of GDGTs related proxies. The geographical isolation of the Baltic Sea, its relatively small size, its particular physical and chemical properties (salinity, oxygen) and the existing long-term monitoring time-series represents a unique opportunity to study in details the functioning and application of GDGT-based proxies for brackish and redox-sensitive marginal seas. First, representative soil and river samples from the drainage basin, monthly resolved sediment trap samples, water column samples and surface sediments from the Baltic Sea will be analysed in order to better constrain the origin, season and depth of GDGTs production. Temperature experiments will also be conducted on an enrichment culture of Thaumarchaeota from the Baltic Sea. Second, short sediment cores from oxic and anoxic basins of the Baltic Sea will be analyzed to compare proxy-based temperature estimates with instrumental data over the last 50 years and to assess the potential effects of changing redox conditions and NH4+ concentrations on GDGT-based proxies. Finally, in order to extend the records beyond the instrumental period and to obtain new insights on the climate variability of the Baltic Sea region over the last 2000 years at a multi-decadal to decadal timescale, GDGT-based proxies will be applied on long sediment cores together with other biomarkers. The results of TETRABAL should not only help to better understand the functioning of GDGT-based proxies in brackish and redox-sensitive marginal seas, but also shed new light on the relationships between temperature, primary production and hypoxia in the Baltic Sea case study.

Lake Salda, located in the lake district of Turkey (SW Anatolia), is a unique environment due to its present day stromatolite formation. Stromatolites, also called laminated organosedimentary structures, are present from the Archean to the modern, and are considered as the oldest fossils on Earth. Carbonates, particularly stromatolites, are archives of geochemical and climatic conditions when they formed. The purpose of the project is to investigate geochemical, mineralogical and isotopic characteristics of Lake Salda stromatolites to elucidate (1) which biotic and/or abiotic processes are involved in stromatolite formation, (2) how geochemical conditions shapes these processes, (3) to what extend stromatolites carry these influences (biotic fingerprint?), and (4) which climatic information (e.g. water level, temperature) stromatolites may hold. To achieve these goals laboratory and field approaches will be applied. Fossils, living stromatotiles, recent sediments and water samples from the lake will be collected during a field excursion in order to examine microbiological and sedimentological characteristics of stromatolites, and the chemistry of the lake water. Elucidating formation mechanisms (biotic vs. abiotic), mineralogical and isotopic characteristics of these unusual carbonates may provide valuable information about regional paleoclimatic and paleohydrological changes and, most importantly, about the beginning of life on Earth.

P.I: Nurgul BALCI, Istanbul Technical University, Department of Geological Engineering, Istanbul, Turkey (ncenulllik@itu.edu.tr)

Project members: Sena AKCER-ÖN, Muğla Sıtkı Koçman University, Muğla, Turkey; Kürşad Kadir ERIS and Ezgi TOK, Istanbul Technical University, Department of Geological Engineering, Istanbul, Turkey; Jérôme KAISER, IOW, Warnemünde (Germany)

Project funded by Istanbul Technical University - Research Division (Grant ITU–BAP-40585 to NB)