Neogene Radiolarian Climate Sensitivity and its Implications for Ocean Ecosystems and Geochemical Cycling
Abstract
The goal of this study was to document and compare radiolarian diversity dynamics at low versus high latitudes, to assess the ecological impacts of differential regional climate change during the Late Neogene. Radiolarians are siliceous protists, which live throughout the ocean water column in a wide variety of trophic niches. They have been among the top silica biomineralizers since the Cambrian, and also constitute a significant component of the marine carbon reservoir. Radiolarians are important exporters of photic zone carbon into the deep ocean through their consumption and aggregation of phytoplankton, thereby helping to regulate global climate. Despite their critical role in the oceans, radiolarians' Neogene and Quaternary biodiversity, biogeography, and sensitivity to climate remain poorly understood. New DNA barcoding studies suggest that modern radiolarian assemblages are more than twice as diverse as estimates in the Neptune microfossil database, and the associated World Register of Marine Species. To rectify this, we generated the first reasonably-complete record of radiolarian diversity from the tropical eastern Pacific from 10-0 Ma, for comparison to a similar published census from the Southern Ocean. Large sample sizes (~5000 specimens) were examined to ensure the documentation of rare species. Our results indicate that tropical radiolarian diversity and community structure were remarkably high and stable throughout the Late Neogene (average diversity = 490 taxa, sd = 22; average evenness (Pielou equitability index) = 0.84, sd = 0.02). This stability was observed in spite of a gradual ~3°C decrease in SST over the last 10 Ma, indicating that this was below tropical radiolarians' sensitivity threshold. By contrast, a major extinction of ~1/3 of Southern Ocean taxa correlates with a ~7°C SST drop from 5-0 Ma. These findings suggest that the relatively greater magnitude of high latitude climate change elicited a significant extinction event and re-organization of radiolarian communities. With projected climate change similar in scale to that of the Late Neogene, we predict elevated extinction risk for high latitude radiolarians in the imminent future. This will likely have consequences for marine food webs and silica cycling, and may reduce the export efficiency of the biological carbon pump.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B22B..02T
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0448 Geomicrobiology;
- BIOGEOSCIENCES;
- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCES