Sensitivity of benthic foraminiferal species in intermediate and deep waters of the tropical western Pacific Ocean to water mass changes
Abstract
We investigate benthic foraminiferal species assemblages as tracers for intermediate to deep-water masses in the tropical Pacific Ocean (International Ocean Discovery Program Expedition 363). In the core tops of the nine study sites (U1482-U1490), the distribution of lower bathyal and upper abyssal species can be separated into two groups, a group that reflects relatively warm (>3.5◦C) intermediate depth water with higher carbon flux (>3.5 g C m-2 year-1) (Bolivina robusta, Bulimina aculeata, Cibicidoides bradyi, C. pachyderma, Cibicides spp., Globobulimina pacifica, Hoeglundina elegans, Laticarina pauperata) versus a group that reflects the colder, deeper waters with lower carbon flux (Oridorsalis umbontus, Uvigerina bifurcata, and Planulina wuellerstofi). These groups largely agree with the 'warm' versus 'cold' water groups of Lutze et al. (1979). Following the approach of Lutze et al., we calculate an index based on the percent intermediate water species ('warm') with respect to the total, intermediate plus deep-water ('cold') species. This index correlates significantly with carbon flux (r=0.90, P=0.0007) and modern bottom water temperatures (r=0.94, P=0.0002). We apply this index to core catcher samples from the study sites. At two of the sites, down-core variations parallel changes in the abundace of Uvigerina proboscidea, a species that is commonly associated with a high carbon flux supporting the use of this index as a productivity proxy. At intermediate water Site U1482 on the northwestern Australian margin where the carbon flux is relatively low and U. proboscidea are absent in the core catchers, down-core variations in the index are similar to long-term changes in Mg/Ca ratios in the upper circumpolar deep water in the South Atlantic Ocean (Billups and Scheiderich, 2009). We speculate that this result might point toward the use of this index as a water mass tracer in regions where in situ primary productivity and carbon flux remain low.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP51C1394E
- Keywords:
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- 1616 Climate variability;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICS