Space, time, seasonality, and the biological synchrony of marine and terrestrial ecosystems of western North America
Impacts of climate variability on marine ecosystems remain poorly described due to the scarcity of biological time series with which to calibrate bio-physical relationships. One way to address this issue is to apply dendrochronology techniques, specifically crossdating, to the annual increment widths of long-lived bivalve and fish species. Resulting chronologies are annually resolved (one value per year), exactly placed in time, and can therefore be readily integrated across species, sites, or with observational records of phenology, movement, or community composition. In so doing, the role of climate forcing and the synchrony it imparts can be examined within and among ecosystems and across a range of temporal and spatial scales.
In the California Current (CC) along the coast of western North America, north winds lift deep, nutrient-rich waters into the photic zone, stimulating primary production. A network of marine fish chronologies and records of seabird reproductive success significantly covaries and can be subdivided into two “guilds:” one that strongly correlated to a winter “mode” of upwelling dominated by high-frequency, interannual variability and another that strongly correlates to a summer “mode” of upwelling dominated by decadal-scale variability. In contrast to summer upwelling, which appears to be driven by fine spatial and temporal atmospheric processes, winter upwelling is driven by broad-scale variability in atmospheric pressure over the northeastern Pacific. These broad- atmospheric patterns also block or facilitate onshore flows of precipitation and thereby drive significant relationships among fish growth, seabird reproductive success, and moisture-sensitive tree-ring chronologies, enabling a 600-year reconstruction of this wintertime climate pattern. On a broader scale, winter climate variability induces inverse covariance between rockfish chronologies in the CC and Gulf of Alaska. Warm years in the northeast Pacific are associated with reduced upwelling in the CC, but increased water-column stability that favors primary production off the British Columbia and southeast Alaska coastline. Overall, these results demonstrate that CC upwelling occurs in unrelated seasonal modes with contrasting trends, atmospheric forcing mechanisms, and impacts on the biology. Moreover, the winter climate pattern is driven by broad-scale variations in sea-level pressure that induce covariability with adjacent terrestrial and marine ecosystems. This underscores the importance of considering seasonality, the potential differences in spatial and temporal scales between seasonal “modes,” and the ability of climate to synchronize biological processes from alpine forests to benthic marine fish.