Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf

Andrew C Thomas,M Elisabeth Henderson,Janet A Nye,Andrew J Pershing,Michael A Alexander,Ryan Weatherbee,Katherine E Mills,Kevin D Friedland,Nicholas R Record,Ken Drinkwater,Jody W Deming

doi:10.1525/elementa.240

Abstract

The northeastern North American continental shelf from Cape Hatteras to the Scotian Shelf is a region of globally extreme positive trends in sea surface temperature (SST). Here, a 33-year (1982–2014) time series of daily satellite SST data was used to quantify and map spatial patterns in SST trends and phenology over this shelf. Strongest trends are over the Scotian Shelf (&gt;0.6°C decade–1) and Gulf of Maine (&gt;0.4°C decade–1) with weaker trends over the inner Mid-Atlantic Bight (~0.3°C decade–1). Winter (January–April) trends are relatively weak, and even negative in some areas; early summer (May–June) trends are positive everywhere, and later summer (July–September) trends are strongest (~1.0°C decade–1). These seasonal differences shift the phenology of many metrics of the SST cycle. The yearday on which specific temperature thresholds (8° and 12°C) are reached in spring trends earlier, most strongly over the Scotian Shelf and Gulf of Maine (~ –0.5 days year–1). Three metrics defining the warmest summer period show significant trends towards earlier summer starts, later summer ends and longer summer duration over the entire study region. Trends in start and end dates are strongest (~1 day year–1) over the Gulf of Maine and Scotian Shelf. Trends in increased summer duration are &gt;2.0 days year–1 in parts of the Gulf of Maine. Regression analyses show that phenology trends have regionally varying links to the North Atlantic Oscillation, to local spring and summer atmospheric pressure and air temperature and to Gulf Stream position. For effective monitoring and management of dynamically heterogeneous shelf regions, the results highlight the need to quantify spatial and seasonal differences in SST trends as well as trends in SST phenology, each of which likely has implications for the ecological functioning of the shelf.

Highlights

Sea surface temperatures (SST) on the North American continental shelf from Cape Hatteras to Nova Scotia (Figure 1) exhibit one of the strongest warming trends of the global ocean (Burrows et al, 2011; Pershing et al, 2015; Saba et al, 2015), and the region has recently been subjected to a strong heat wave (Mills et al, 2013; Scannell et al, 2016)
Quarter-degree spatial resolution SST data over the northeastern North American shelf have provided the regional geography of overall warming rates not evident in previous work
We have shown that these SST warming rates exhibit strong seasonal biases at many locations

Summary

Introduction

Sea surface temperatures (SST) on the North American continental shelf from Cape Hatteras to Nova Scotia (Figure 1) (hereinafter referred to as the northeastern shelf) exhibit one of the strongest warming trends of the global ocean (Burrows et al, 2011; Pershing et al, 2015; Saba et al, 2015), and the region has recently been subjected to a strong heat wave (Mills et al, 2013; Scannell et al, 2016). Maynard et al, 2016; Stephenson et al, 2009). Such trends impose serious challenges for fisheries and fisheries management Friedland and Hare (2007) show increasing annual SST ranges over the northeastern shelf in the later years of their 1854–2005 time series. Such changes in SST phenology can drive changes in species phenology that potentially have large ecosystem ramifications when shifts among functionally linked aspects of the food web

Results

Discussion

Conclusion