Benthic foraminifer diversity in the Santa Barbara Basin from 1834-2008

Abstract:

Accelerating industrialization and a worsening climate crisis are leading to an increasingly uncertain future for marine ecosystems. While the fossil record can inform long-term (>10³ year) expectations for ecosystem outcomes under multiple climate scenarios, making near-term predictions is more difficult. At present, we lack sufficiently detailed records of historical and modern ecosystem baselines to assess the impact of 19^th through 21^st century industrialization on benthic marine ecosystem diversity. This severely limits our ability to understand and predict the decadal- to centennial-scale impacts of the current climate crisis. However, exceptionally-resolved fossil records have the potential to fill this critical knowledge gap.

The Santa Barbara Basin (SBB) in Southern California preserves varved sediments in annual layers due to prevalent bottom-water anoxia that prevents bioturbation of these annual layers. These yearly records provide a high-resolution glimpse into the climatic and ecosystem trends over the last 200 years. To date, the SBB has been instrumental in constructing high-resolution records of climate (temperature, precipitation, etc.) and pelagic ecosystem trends (planktonic foraminifera, fish scales and otoliths), yet no studies have leveraged these records to examine annual trends in benthic diversity.

Here we present a record from box core MV1012 that details trends in foraminifer diversity from 1834 to 2008 CE. This annual record allows for study of benthic marine ecosystem structure at an unprecedented resolution during a time when anthropogenic impacts were exponentially increasing in Southern California. Preliminary analyses indicate that late 19^th and early 20^th century assemblages are comprised primarily of species within the genus Bolivina and similar morphotypes (“bolivinids”). During the mid-20^th century (1950-1960), we observe a shift from assemblages with high bolivinid dominance to assemblages with higher evenness and lower individual abundance, gradually shifting towards late 20^th-century assemblages that are increasingly dominated by Nonionella stella. These assemblage shifts may reflect the impact of environmental changes resulting from California’s post-WWII industrialization on SBB benthic marine diversity.