Examining the potential of Pacific abalone as a novel high-resolution archive of upwelling in the California Current

Abstract

Upwelling is a dynamic oceanographic process that brings cold, nutrient-rich waters to the surface. These nutrients encourage primary productivity, forming the foundation of coastal food webs and the fisheries depending on them. Understanding past variability in the occurrence of upwelling and primary productivity may offer insight into how upwelling dynamics and ecosystem productivity could vary in the future. Numerous proxies from sediment cores inform most upwelling reconstructions; however, their temporal resolution is typically decadal at best. However, questions regarding ecosystem responses to changes in physical processes require data with seasonal to sub-seasonal resolution because such data provide additional insight into seasonal extremes (e.g., surface temperature, precipitation, etc.). The calcium carbonate skeletons of mollusks provide invaluable data from stable oxygen (δ18O) and carbon (δ13C) isotopes that generate high-resolution reconstructions of environmental variables. Recent studies of stable nitrogen (δ15N) isotopes in mollusk shell organic materials demonstrate the potential to produce high-resolution reconstructions of nutrient cycling. Collectively, these measurements may provide insight into upwelling conditions over the life of the organism. This study presents preliminary data exploring the potential of analyzing a suite of stable nitrogen, oxygen and carbon isotope data from analysis of Pacific abalone shells (Haliotis cracherodii). We present sub-seasonal δ15N time series data that, together with δ18O and δ13C, reflect seasonal variability closely linked to upwelling. δ15N values range from 8.3‰ to 11.0‰ and align closely with δ18O values, which range from −0.5‰ to 1.1‰. Implications of this research are twofold: 1) Isotopic analyses from abalone shells may provide detailed knowledge on primary productivity during upwelling as well as limited productivity when upwelling is greatly reduced and 2) archaeological shell middens in the Channel Islands contain an abundance of both abalone dating back to the early Holocene, presenting the opportunity to reconstruct upwelling conditions throughout the Holocene.