Planktic foraminifers of the California Current at 42°N : last glacial maximum and present

Graduation date: 1996MOCNESS plankton tows, sediment traps and sedimentary material are used to determine\ud the linkage between bio-physical forcing and foraminiferal response over a range of time\ud scales from the event scale to the glacial interglacial cycle. The annually averaged planktic\ud foraminiferal fauna of the modem California Current is a diverse community composed of\ud individuals from subarctic, transitional, and subtropical foraminiferal assemblages. This\ud community is more diverse, but less abundant in total standing stock and shell flux than the\ud subarctic community of the Gulf of Alaska. The use of plankton tow and isotopic data\ud allow us to partition the foraminiferal community into shallow dwelling euphotic zone\ud species and deep dwelling sub-thermocline species. On both the event and seasonal time\ud scales, heterotrophic species were most abundant in cold, biomass rich coastal waters. In\ud contrast, species which harbored endosymbionts were more abundant in oligotrophic\ud waters with higher ambient light levels. During the Last Glacial Maximum (LGM), the\ud diverse modern fauna was replaced with a low diversity, high flux, heterotrophic\ud community similar to that of the modern Gulf of Alaska. Modern analog temperature\ud estimates suggest the California Current was roughly 3°C cooler during the LGM than\ud today. Coupled with oxygen isotopic results from G. bulloides, the surface thermal\ud structure implies an equatorward flowing glacial California Current at these sites. The\ud Polar Front thus remained north of these locations during the LGM. Comparison of glacial\ud G. bulloides carbon isotopes and shell accumulation rates with organic carbon flux\ud estimates implies the glacial California Current was (1) higher in nutrient content, (2) lower\ud in plankton biomass, and (3) lower in export carbon flux than its modem counterpart. This\ud description suggests that during the LGM the plankton community of the California Current\ud was very similar to the modern plankton community of the Gulf of Alaska