Physical control of the distributions of a key Arctic copepod in the Northeast Chukchi Sea

Abstract

The copepod Calanus glacialis is one of the most important zooplankton taxa in the Arctic shelf seas where it serves as a key grazer, predator, and food source. Its summer distribution and abundance has direct effects on much of the food web, from blooming phytoplankton to migrating bowhead whales. The Chukchi Sea represents a highly advective regime dominated by a barotropicly driven northward flow modulated by wind driven currents that reach the bottom boundary layer of this shallow environment. In addition, a general northward gradient of decreasing temperature and food concentration leads to geographically divergent copepod growth and development rates. The physics of this system establish the connection potential between specific regions. Unless biological factors are uniform and ideal the true connections will be an uneven subset of this physically derived connection potential. In August 2012 and 2013, C. glacialis distributions were observed over Hanna Shoal in the northeast Chukchi Sea. Here we used the Finite Volume Community Ocean Model i-State Configuration Model to advect these distributions forward and back in time to determine the source and sink regions of the transient Hanna Shoal C. glacialis population. We found that Hanna Shoal supplies diapause competent C. glacialis to both the Beaufort Slope and the Chukchi Cap, mainly receives juveniles from the broad slope between Hanna Shoal and Herald Canyon and receives second year adults from as far as the Anadyr Gulf and as close as the broad slope between Hanna Shoal and Herald Canyon. These connection potentials were not sensitive to precise times and locations of release, but were quite sensitive to depth of release. Deeper particles often traveled further than shallow particles due to strong vertical shear in the shallow Chukchi. The 2013 sink region was shifted west relative to the 2012 region and the 2013 adult source region was shifted north relative to the 2012 region.

Impact of a warm anomaly in the Pacific Arctic region derived from time-series export fluxes

“…Whereas Pacific copepods were not collected in 2019 despite the enhanced transport of Pacific waters observed until September 2019 across Bering Strait [ 7 ], the sustained inflow of warmer waters resulted in the near absence of Calanus at DBO2 and DBO3 during June and July 2019. While the majority of Calanus copepods present in the Chukchi Sea are believed to originate from the Bering Sea [ 38 ], their increasing abundance at DBO4 in July 2019 suggested an alternate source of Calanus on the northern Chukchi shelf during summer 2019 [ 63 ]. No clear peaks in copepod abundance were observed during June or July 2019, consistent with high seasonal and interannual variability in the Pacific Arctic region [ 62 ].…”

Multi-scale temporal variability in biological-physical associations in the NE Chukchi Sea

“…Zooplankton communities in the Hanna Shoal area are dominated numerically by small copepods such as Oithona similis and Pseudocalanus spp. and in biomass by the larger Calanus glacialis/marshallae (Lane et al 2008;Elliott et al 2017;Lalande et al 2020). The Arctic copepod Calanus hyperboreus has also been observed in this area (Lane et al 2008;Hopcroft and Day 2013;Lalande et al 2020).…”

“…In winter, high abundances of O. similis copepods and lower abundances of stage five copepodites of C. glacialis were observed in sediment trap samples obtained at the CEO (Lalande et al 2020). O. similis has been reported to perform small scale DVM in the Arctic (Ashjian et al 2003;Daase and Falk-Petersen 2016) whereas stage five copepodites of C. glacialis enter diapause to overwinter at depth (Falk-Petersen et al 2009;Elliott et al 2017) and would not contribute to an acoustically-detected DVM signal in winter.…”