PLANKTIC FORAMINIFER TEST SIZE DURING THE NEOGENE: PALEOENVIRONMENTAL RESPONSE IN THE ATLANTIC OCEAN

Pelagic carbonate is an important part of the Earth’s climate processes; it acts as a large but reactive reservoir of carbon dioxide. Planktic foraminifera make up a significant part of the open ocean’s contribution. Understanding if their contribution has been consistent is an important facet in our understanding of the carbonate cycle. To that end, we have generated new records of planktic foraminiferal test size and accumulation over the past ~7 myrs at several scientific ocean drilling sites from the Atlantic Ocean. Samples were imaged using automated microscope systems and analysed using Olympus Stream Viewer software to identify foraminifer tests and detect their sizes. Two sites, Ocean Drilling Program (ODP) Site 925 in the tropical atlantic and Integrated Ocean Drilling Program (IODP) Site U1313 at the northern edge of the subtropical gyre, were analysed at high resolution (0-3 Ma, ~3 kyr resolution) to examine Milankovitch-scale orbital forcing. The two others are lower resolution (10’s of kyr resolution) but were paired with existing data to determine their response to specific paleoenvironmental parameters. ODP Site 659 is frequently inundated with dust or siliciclastic input from the Sahara while IODP Site U1396 has many tephra layers due to its location near Montserrat. Both volcanic and terrestrial input are possible external sources of nutrients likely to give rise to elevated phytoplankton primary productivity. A fragmentation index record was generated for each site to examine if changes in size were biased by dissolution. Orbital forcing in both the sub-precession and precession bands were detected at a statistically significant level. At Site 659 a size increase is concomitant with increased terrestrial input, likely resulting in increased local productivity.