North Atlantic summers have warmed more than winters since 1353, and the response of marine zooplankton

Abstract

Modeling and measurements show that Atlantic marine temperatures are rising; however, the low temporal resolution of models and restricted spatial resolution of measurements (i) mask regional details critical for determining the rate and extent of climate variability, and (ii) prevent robust determination of climatic impacts on marine ecosystems. To address both issues for the North East Atlantic, a fortnightly resolution marine climate record from 1353-2006 was constructed for shallow inshore waters and compared to changes in marine zooplankton abundance. For the first time summer marine temperatures are shown to have increased nearly twice as much as winter temperatures since 1353. Additional climatic instability began in 1700 characterized by ∼5-65 year climate oscillations that appear to be a recent phenomenon. Enhanced summer-specific warming reduced the abundance of the copepod Calanus finmarchicus, a key food item of cod, and led to significantly lower projected abundances by 2040 than at present. The faster increase of summer marine temperatures has implications for climate projections and affects abundance, and thus biomass, near the base of the marine food web with potentially significant feedback effects for marine food security.coralline algae | rhodolith | maerl | seasonal P rior to instrumentally derived temperature records that began in the 1850s, knowledge of seasonal and regional-scale marine temperature changes at high latitudes is limited. Thus at present, hemispheric Atlantic climatic patterns are deduced from multiproxy and instrumental networks using statistical (1, 2) and modeling (3) approaches. Whereas such approaches show that the Atlantic Multidecadal Oscillation (AMO), the North Atlantic Oscillation (NAO), and Atlantic Meridional Overturning Circulation (AMOC) have a substantial influence on Atlantic climate (e.g., ref. 4) they are still unable to capture details that are critical for determining the spatiotemporal distribution of climate oscillations (5, 6) and their associated impacts (7). For example, whereas the AMO, which models suggest reflects multidecadal variation in the AMOC (8), is the dominant influence on summer climate in the United Kingdom (9), at higher European latitudes, seasonal terrestrial tree-ring climate records (6, 10) are not representative of high-latitude sea surface temperatures (11). Limited spatiotemporal resolution, absent proxy validation and organism effects have restricted the distribution of current inshore proxy-derived sea surface temperature (SST) records (12-16). Therefore to date, we have a poor understanding of season specific temperature variability. Similarly, SST, AMO, and AMOC variations are not well represented at high spatiotemporal resolution beyond the instrumental record in North East Atlantic shallow inshore waters (for example 55°50'N 05°50'W). This information is needed to better understand rates of regional climate variability (5).Marine responses to such climate fluctuations are reflected in the productivity of marine ecosystems f...

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