Hikurangi Trough late Pleistocene palaeoceanography, biostratigraphy and Cretaceous Ocean Anoxia Events (OAEs)

Part I:

The regions of the world's oceans, which border Antarctica, are critical for controlling the Earth's climate. Firstly, the largely unhindered transit of ocean currents (the Antarctic circumpolar current, ACC) that circle and Antarctic continent enables the continued maintenance of its huge continental ice sheets. Secondly, a permanent thermal boundary between water masses extends to the ocean surface within the Subtropical Convergence (STC) in this region. Consequently, this is a region of high biological productivity due to the mixing of micronutrient-rich subtropical waters (STW) with macronutrient-rich subantarctic waters (SAW). As such the STC is a highly important sink for atmospheric CO2 due to high levels of primary productivity.

This region is also influenced by the presence and extent of the Western Antarctic Ice Sheet (WAIS). The extent of this ice sheet has been shown to alter the latitudinal positioning of the Southern Hemisphere STC by up to 7 degrees from stadial-interstadial cycles of the Late Pleistocene epoch (last 800 ka), and may subsequently partially decouple global climate from atmospheric partial pressure of carbon dioxide. Previous studies highlighting the Late Pleistocene evolution of sea surface and intermediate waters within the southwest Pacific have indicated complex behaviour of the subtropical front (STF) throughout this interval.

Utilizing samples from site U1520D from within the Hikurangi Trough (Expedition 375), we propose a high resolution (<1 kyr) study of late Pleistocene foraminifera to better constrain the regional paleoceanography over the last 130 ka, and how this relates to climate forcing. We aim to better understand the STC through paired measurements of oxygen isotopes and Mg/Ca trace element ratios of both planktonic (Globigerina bulloides) and benthic foraminifera (Uvigerina peregrina). G. bulloides is a symbiont-barren, opportunistic species which often dominates the foraminifer fauna, and sediment assemblage of the ocean floor, and is therefore an important source of geochemical information for palaeoceanographic studies. U. peregrina is an infaunal benthic species, which has also been used extensively to calculate intermediate water properties throughout the Pliocene-Pleistocene. These stable isotope and trace metal records are required to assess the scale and timing of surface and intermediate water temperature, and salinity across the STC. This data will subsequently contribute to our knowledge of the extent and influence of the WAIS and meridional gradient variability response to orbital forcing during a critical period of cryosphere development.

Part II:

The Cenomanian-Turonian boundary (CTB) can be correlated globally in pelagic carbonate facies by a major turnover in fossil groups, and by a positive carbon isotope excursion, typically associated with dark marls or shales enriched in organic carbon. The dramatic changes within lithology are attributed to increased rates of oceanic-turnover and upwelling of nutrient-rich deep water masses, and high surface-water productivity.
Oxygen depletion and eutrophication of the Earth's oceans has been associated with warming in the geological past, and current observations show expansion of modern oxygen minimum zones. Clarifying the nature and mechanism of these oceanic anoxia events (OAEs), and there effect upon life is imperative to our understanding the possible implications that anthropogenic climate forcing may have upon the biodiversity of the modern ocean.
We plan to utilize samples sourced from IODP Expedition 375 Hole 1520C, within the Hikurangi Trough, where an expanded section is been identified detailing the Cenomanian-Turonian boundary. Through foraminiferal faunal analysis and paired measurements of oxygen and carbon isotopes we aim to elucidate the nature of the CTB within the Hikurangi Trough, which represents a rare, well-preserved high-latitude example of a Cretaceous OAEs.

The key impacts will be the multi-disciplinary benefits to the over-arching academic community, the research outcome has a large scope for input into international policy and procedure, especially in reference to climate science. Most notably, there are currently huge efforts to better understand and predict the possible outcomes of continued anthropogenic climate forcing. Well-recovered, high-resolution (<1 kyr) records from the last glacial-interglacial cycle are imperative to provide high-quality data for inferences for more accurate climate reconstructions, to better constrain our understanding of future anthropogenic forcing. The Intergovernmental Panel on Climate Change (IPCC) will be of direct benefit from the data acquired, which will contribute towards future IPCC Assessment Reports, and consequently be accessory to possible future mitigation efforts.

The taxonomic and biostratigraphic framework which will be constructed through the post-cruise research efforts, by the PGR as well as the entire chronostratigraphic team, will yield vital contributions to the process of constructing the Atlas of Neogene Planktonic Foraminifera in the coming years. Building on from the huge success of the formation of the Palaeogene atlases, the publication is vital to the micropalaeontological and palaeoceanographic community, but specifically to research students in planktonic foraminifers. Additionally, the atlas will be used extensively within the petroleum sector, being the standard reference used by the industry for Neogene biostratigraphy.

The PGR will also be participating in multiple public outreach events including Lyme Regis and Yorkshire Fossil Festivals in the years to come, which will allow us to ensure the objectives of the expedition research, and the IODP as a whole can be promoted readily to the public, and encourage public engagement within the scientific community. These festivals have been incredibly effective in the past, especially when promoting regional and global scientific efforts to local schools and families.