PP43D-01 INVITED
Arctic coring expedition: how to beat the system and win
The genesis of the Arctic Coring Expedition (ACEX) was, appropriately enough, centered on the bold and seminal scientific goal of recovering the first Cenozoic geological record from the Arctic Ocean. The expedition, however, would not have occurred, let alone succeeded, without concomitant efforts to create a new programmatic framework (the Integrated Ocean Drilling Program), to determine, and convince others of the feasibility of the novel, 3-ship program, to plan and budget the logistical and operational aspects, to identify key entities and personnel, to secure financial backing on the order of 13 million dollars, and to manage the expedition in real time. To embolden others, the authors will share their trials and tribulations as well as choice personal anecdotes.
PP43D-02 INVITED
The Cenozoic Arctic Ocean Unveiled through Scientific Ocean Drilling
In late summer 2004, the Integrated Ocean Drilling Program (IODP) conducted one of the most transformational missions in the almost 40 year history of scientific ocean drilling: the Arctic Coring Expedition (ACEX). This technically-challenging expedition recovered the first Cenozoic sediment record from the Arctic Ocean-extending previous records from ~1.5 Ma to an unprecedented ~56 Ma. Glimpses of the breadth of this transformation were even seen during ACEX when the massulae from fresh water ferns were found and the presence of Apectodinium augustum confirmed that the Paleocene-Eocene Thermal Maximum (PETM) was unexpectedly recovered. Soon after the expedition, when the cores were opened and analyzed, ice-rafted debris was found to have occurred much earlier than previously thought-in the Eocene in an environment of high organic carbon content. The initial analyses also revealed an extensive hiatus that occurred between several of the most spectacular sediment cores in terms of color, e.g. turquoise, and structure, starkly contrasting black and white crossbedding that is now dubbed the "zebra" core. The exciting early results attracted other investigators that expanded the scientific investigating team to more than 40 people. This, in turn, extended the analyses to include new studies that revealed surprisingly high Arctic Ocean surface water temperatures and a hydrologically active system during the PETM. Although the hiatus is a lost window in time for the Arctic paleoclimate record, it spawned other studies that integrated the regional tectonic history with ACEX results revealing a major oceanographic reorganization at 17.5 Ma-ventilation of the Arctic Ocean to the North Atlantic through the Fram Strait. In this overview, recent results from the large ACEX scientific "family" are summarized and include: a new age model; detailed analyses of the middle Eocene that document a unique brackish water environment; sea ice and iceberg history reconstructions and provenance from the Eocene to present; evolution of depositional environments that are linked to broader tectonic & subsidence histories; times of isolation and connection to the global ocean; geochemical analyses of the organic carbon-rich sediments; and unique applications of high resolution proxies and cyclostratigraphy.
PP43D-03 INVITED
Neogene and Eocene Ice-Rafting in the Central Arctic
The Cenozoic ice-rafted debris (IRD) history of the central Arctic is reconstructed utilizing the terrigenous coarse sand fraction in IODP 302 cores from 0-273 mcd, which spans the depth range of the granule/pebble distribution in the split cores identified by the scientific party. This Holocene-middle Eocene quantitative record of terrigenous sand accumulation on the Lomonosov Ridge, along with qualitative information on grain texture and composition, confirm the interpretation that ice-initiation (sea ice and glacial ice) occurred ~46 Ma in the Arctic, and provides a long-term pattern of Arctic ice-expansion and decay since the middle Eocene. IRD mass accumulation rates range from 0 to 0.13 g/cm2/kyr in the middle Eocene and from 0 to 0.36 g/cm2/kyr in the Neogene. IRD MAR maxima in the Miocene and Pliocene co-occur with either glacial initiations or intensifications in the sub-Arctic. Patterns of high IRD flux in the Eocene are compatible with obliquity forcing (Sangiorgi et al., in press). A quasi-cyclic pattern of IRD input since 14 Ma with a frequency between 0.5-2 myr, suggesting that Arctic ice growth and decay was also influenced by long-term eccentricity forcing. The 46.25 Ma IRD onset in the central Arctic slightly precedes the earliest evidence of ice in the Antarctic, and compares in timing with a 1000 ppm decrease in atmospheric concentrations of CO2. The decline of pCO2 in the middle Eocene may have driven both poles across the temperature threshold that enabled the nucleation of glaciers on land and partial freezing of the surface Arctic Ocean, especially during times of low insolation.
PP43D-04 INVITED
Fresh and Warm Arctic Ocean Surface Waters During Eocene Thermal Maximum 2
Eocene Thermal Maximum 2 , at about 53.5 Ma (further referred to as the Elmo phase), was a short-lived (approximately 50 kyr) episode of widespread deep sea carbonate dissolution and warming. The few published records suggest that climate change during the Elmo phase was similar to the well known Paleocene-Eocene thermal maximum (PETM) at 55.5 Ma, but of a smaller magnitude. The Elmo phase was only recently discovered and the lack of climate records inhibits detailed description of the global change, as well as comparison to the PETM. We present micropaleontological (dinoflagellate cyst), organic geochemical (TEX86, BIT, stable carbon isotopes of bulk organics and n-alkanes) and inorganic geochemical (XRF) data from the Elmo section recovered from the Lomonosov Ridge, Arctic Ocean, during IODP Expedition 302 (ACEX). The stable carbon isotope record on total organic carbon (TOC) shows a 3.5 ‰ negative carbon isotope excursion at the onset of the Elmo, 1 to 1.5 ‰ smaller than that usually recorded in TOC for the PETM. Dinocyst assemblages show a freshening of Arctic Ocean surface waters, while TEX86-derived paleotemperatures show a rise from about 18 to 22 ° C. Moreover, laminated sediments and the absence of organic foraminiferal linings suggest that anoxia developed at the sediment-water interface. Biomarker analyses also indicate euxinic conditions in the photic zone. All trends, including those recorded using XRF core scanning techniques, mimic those observed during the PETM but exhibit a slightly smaller magnitude. Our findings, together with the scant published data, corroborate the notion that the Elmo was indeed a true global warming phase, associated with the rapid injection of light carbon.
PP43D-05
Cold Late Oligocene Arctic Ocean: faunal and stable isotopic evidence.
Global cooling in the Early Oligocene was an important defining point in the evolution of the global Cenozoic climate. New evidence from arctic Alaska provides insights into the extent and degree of Oligocene cooling of the northernmost ocean. Paleotemperature data from this critical interval are missing from the deep sea cores recently recovered from the central part of the Arctic Ocean. Our new evidence comes from the Nuwok Member of the Sagavanirktok Formation on the North Slope of Alaska, dated as late Oligocene based on benthic foraminifera and Sr isotopes. The taxonomic composition of the abundant late Oligocene biota suggests that a relatively cold marine climate prevailed there and has persisted in the Arctic Ocean to the present day. A notable and unique aspect of the Nuwok molluscan fauna is that all but one of its genera still live in the Arctic Ocean. On the other hand, in contrast to Oligocene deposits worldwide, the Nuwok beds contain only one species that is a remnant of cosmopolitan Paleogene faunas. The oxygen stable isotopic record of the benthic bivalves Thyasira alaskana and Arctica carteriana from the Nuwok type section support a seasonal range of sea surface temperatures from 1.04 to 9.2 deg C. Late Oligocene Arctic Ocean temperatures appear to be slightly warmer than the Beaufort Sea today, but significantly colder than most Paleogene sea-surface temperatures. These data strongly imply that the Arctic Ocean became cold much earlier than previously thought. Our preliminary data suggest that the Arctic Ocean may have been a significant evolutionary center for arctic mollusks. As a result of dwelling in a continuously cold ocean, Arctic Ocean mollusks did not evolve as fast, or as profoundly, from the late Oligocene to the Holocene, as have mollusks elsewhere in the world ocean.
PP43D-06
Biomarker Constraints on Arctic Surface Water Conditions During the Middle Eocene
Through analyses of unique microlaminated sediments of Arctic drill cores, recovered from the Lomonosov Ridge in the central Arctic Ocean during Integrated Ocean Drilling Program (IODP) Expedition 302, it has been shown that enormous quantities of the free floating freshwater fern \textit {Azolla} grew and reproduced in situ in the Arctic Ocean during the middle Eocene (Brinkhuis et al., Nature, 2006).The presence of the freshwater fern Azolla, both within the Arctic Basin and in all Nordic seas, suggests that at least the sea surface waters were frequently dominated by fresh- to brackish water during an interval of at least 800 kyr. However, to which degree the Arctic Basin became fresh and what the consequences of these enormous Azolla blooms were for regional and global nutrient cycles is still largely unknown. Comparing samples of extant Azolla, including its nitrogen fixing symbionts, with samples from the Arctic Azolla interval revealed the presence of a group of highly specific biomarkers. These biomarkers are closely related to similar organic compounds that have been suggested to play a crucial role in the biogeochemistry of nitrogen fixing bacteria. This finding, therefore, potentially implies that this symbioses dates back to at least the middle Eocene. Furthermore, this particular symbiosis was probably crucial in triggering basin wide Azolla blooms. We now aim to measure compound specific stable hydrogen isotope values of these biomarkers which should provide insight into the degree of mixing between high salinity (isotopically heavy) deeper and low salinity surface water (isotopically light). The results of these compound specific isotope analyses will be extrapolated using calibrations from controlled growth experiments and subsequently evaluated using climate modeling experiments.