Can deep ocean circulation pathways and strength be reconstructed using marine sediment dispersion?

Date & time

1–2pm 24 May 2018

Location

Jaeger 1 Seminar Room, RSES

Speakers

Alexander Piotrowski (University of Cambridge)

Event series

Contacts

 Adele Morrison

Ocean circulation plays a key role in the Earth’s climate system because surface ocean currents transport heat and deep ocean water masses can sequester carbon dioxide from the atmosphere.  Geochemical proxies measured on carbonate foraminifera picked from marine sediments have been widely utilized to reconstruct past ocean changes.  However, it is difficult to use the proxies to unambiguously reconstruct deep water circulation, because they are controlled by biological productivity and chemical cycling in addition to water mass advection.  Here I present a method to reconstruct large-scale ocean advection by measuring the dispersion of fine detrital silicate sediment which have been separated into specific grainsize fractions across the clay to silt (0-63 mm) range.  We have initially applied this technique in the North Atlantic and Southern Ocean.  The North Atlantic hosts a strong geostrophic current that transports sediment from geological sources with distinct and well-constrained geochemistry (i.e. Iceland and the Canadian Shield).   The Southern Ocean provides an opportunity to examine the largest wind forced circulation on the planet in an environment where sediments have multiple inputs (hemipelagic, ice rafted, and windblown dust).  Our geochemical data shows that grainsize separation often allows “unmixing” of the silicate component of a single marine sediment sample into at least three differently sourced components, with the finest grainsizes derived from distal sources and transported great distances by deep current flow, while the coarser silt fractions are locally derived.   Time slice reconstruction using modern sediment core-top and down-core samples during the last deglaciation place new constraints on glacial-interglacial changes in sediment sources and ocean circulation pathways.  This research also raises the possibility of reconstructing ocean circulation changes at locations or time periods where foraminifera do not exist, in older geological periods where sediments have undergone diagenetic alteration, and tracing large-scale dispersion of anthropogenic particulates in the modern ocean.

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