PP034-08
Multi-proxy evidence for a millennial expansion of the south Pacific gyre driven by ENSO/SAM interactions

Friday, 11 December 2020: 20:58
Virtual
Daniel Sinclair1, Nicholas T Hitt2, Helen Neil3, Aimee K Komugabe-Dixson4, Stewart Fallon5, Sarah Bury3, Julie Brown3, Amandine Sabadel3,6, Josette Delgado3 and John Charles Hellstrom7, (1)Victoria University of Wellington, School of Geography Environment and Earth Sciences, Wellington, New Zealand, (2)Victoria University of Wellington, School of Geography, Environment and Earth Sciences, Wellington, New Zealand, (3)National Institute of Water and Atmospheric Research, Wellington, New Zealand, (4)Ministry of Primary Industries, Auckland, New Zealand, (5)The Australian National University, Research School of Earth Sciences, Canberra, Australia, (6)Plymouth Marine Laboratory, Plymouth, United Kingdom, (7)University of Melbourne, School of Earth Sciences, Parkville, VIC 3010, Australia
Recorded Presentation
Abstract:
The South Pacific Gyre (SPG) is the largest ocean gyre on Earth. It modulates Pacific climate by distributing warm, subtropical waters to high latitudes along its western limb and returning cool, subpolar waters back to low latitudes along its eastern limb. In recent decades, acceleration of the SPG’s western boundary currents have increased temperatures in the SW Pacific by up to 4x the global average. This has also altered macronutrient distributions and impacted marine ecology.

These recent changes, however, may not be unprecedented. Here we investigate a possible SPG enhancement between 2000-3000BP by reconstructing SPG circulation strength and bioavailable nitrogen distributions using deep-sea black corals from New Zealand and the Tasman Sea. We use marine radiocarbon reservoir age (∆R) to track the strength and latitudinal extent of southwest SPG boundary currents (Hitt et al., submitted; Komugabe-Dixson et al., 2016). ∆R is low in the subtropical waters and interior of the Gyre due to a greater exchange of 14CO2 between the ocean and atmosphere (Key et al., 2004). We use bulk and amino-acid specific nitrogen isotopes to reconstruct the spatial distribution of bioavailable nitrogen. POM δ15N in the central Gyre is high due to complete NO3- utilization and a lower degree of fractionation during photosynthesis (Somes et al., 2010).

We see a reduction in ∆R and increase in δ15N around between 2000-3000BP, suggesting that Gyre circulation was enhanced and expanded southward. This thousand-year interval of stronger SPG circulation corresponds to a period where ENSO and the Southern Annular Mode (SAM) are coupled (Gomez et al., 2012; Komugabe-Dixson et al., 2016). Both ENSO and SAM modulate the strength of different currents in the SW Pacific. ENSO affects the South Equatorial Current and East Australian Current (EAC) while SAM affects the EAC, EAC Extension and Tasman Front. We therefore conclude that a coupling between ENSO/SAM drove a strengthening and expansion of the SPG that is similar to the Gyre intensification observed in the present day.

<< Previous Abstract | Next Abstract