Seasonal Trends and Preservation Biases of Polycystine Radiolaria in the Northern California Current System

Abstract

We analyzed a 2‐year sediment trap record of 76 species of Radiolaria from three locations across the northern California Current System. Q‐mode factor analysis identifies the fundamental trends in the radiolarian data with a five‐factor model that explains 86% of the trap data. The factor assemblages that emerge from this analysis have temporal and spatial aspects that reflect fundamental oceanographic features of the eastern North Pacific. The most dominant process revealed by this analysis is related to the seasonality of the California Current. Two factors illustrate this: the California Current factor, which has highest loadings during summer and fall, and the Winter factor, which is most important in the winter and spring. Together they account for 75% of the information in the trap samples from the two moorings located in the coastal region extending to ∼300 km offshore. The oceanic environment sampled by the mooring 650 km offshore is strongly influenced by transitional waters and those from the Central and Subarctic Gyres. Loadings of the three factors related to these oceanographic regions show marked differences between years, which illustrates the latitudinal variability in the divergence of the North Pacific Current. Spatial distributions of the trap factors in surface sediments beneath the California Current System generally agree with the temporal and spatial patterns they exhibit in the traps. Nonetheless, the trap factor model can only describe up to 50% of the radiolarian sediment data, which means the species ratios in the sediment traps are significantly different than those in the sediments. A factor model using only robust species reveals the same basic trends as the first analysis, but the culled model is able to describe a larger fraction of the sediment data (63%–91% in sediments directly beneath the mooring sites). However, the increase in the amount of sediment data explained by the culled model is not distributed equally across all factors but is due to very high estimates of one factor in the coastal sediments, the California Current factor. At the Nearshore mooring site (130 km offshore) this factor explains 69% of the sediment data versus only 32% of the data in the traps where it was derived. This discrepancy suggests that either these two years of trap data are anomalous and have underestimated the predominance of the California Current assemblage over long time periods or the culled factor model, rather than eliminating the dissolution bias, actually overemphasizes the importance of well‐preserved species in the coastal environment.