STANDING STOCK BIOMASS OF BENTHIC FORAMINIFERA IN THE SANTA BARBARA BASIN DECREASES IN THE 19TH AND 20TH CENTURIES

Empirical information on biomass trajectories over key periods of environmental variability is necessary for understanding how climate change affects paleocommunity production. Yet while biomass is among the most energetically meaningful metrics of paleocommunity change, it is rarely measured in the fossil record due to the time-intensive nature of these measurements. Further, the extent of time averaging in most typical fossil records precludes the ability to directly relate biomass changes to community production. But without long-term empirical data that spans beyond the recent past, our ability to understand the mechanistic connections between climate change and energy and nutrient flow through marine ecosystems is limited. Here we use a dataset of more than 21,000 measurements of terminal test size from twelve species of benthic foraminifera from the (SBB) as a proxy for standing-stock biomass over an 800-year-long interval. Changes in body size are positively correlated across species, and the strength of these positive correlations increases when populations are primarily comprised of small individuals. When we convert body size to biomass, we find that standing-stock biomass underwent a substantial, punctuated decrease during the mid-19^th and -20^th centuries and has remained low through the present day. Using environmental proxy records from nearby SBB cores, we find that oxygen availability is correlated with increases in biomass throughout this record. However, the decrease we observe in standing-stock biomass is not correlated with a similarly marked oxygen decrease, suggesting that additional factors contributed to changes in energetic capacity within the SBB in the recent past.