The Dynamics of the North Atlantic Subpolar Gyre Introduces Predictability to the Breeding Success of Kittiwakes

Abstract

Since the open-ocean subpolar Atlantic is amongst the most predictable regions in the world, our results hold promise for predicting the general production to seabird populations over a large geographical region adjacent to the northern North Atlantic and the Arctic Mediterranean. Colonies of black-legged kittiwakes Rissa tridactyla in the North Atlantic have declined markedly since the mid-1990s, partly due to repeatedly failing breeding seasons. We show a close link between the breeding success of a kittiwake colony in the Faroe Islands and the subpolar gyre index. Successful breeding follows winters with an expanded subpolar gyre and, by inference, increased zooplankton abundances southwest of Iceland. The environmental conditions in the northwestern Atlantic during the non-breeding and pre-breeding seasons might therefore be important. Furthermore, the subpolar gyre dynamics might influence the local food abundance on the Faroe shelf during the breeding season.

On the Recent Ambiguity of the North Atlantic Subpolar Gyre Index

“…The PC1 presented by Foukal and Lozier (2017, their Figure 2b), resembles Figure 1b, and thus exhibits a more linear trend than any of the previously published gyre index versions (Berx & Payne, 2017;Häkkinen et al, 2013;Häkkinen & Rhines, 2004;Hátún et al, 2005;Hátún, Azetsu-Scott, et al, 2017;Hátún, Olsen, et al, 2017;Larsen et al, 2012). A comparison of some of the previous gyre index versions is provided by Berx and Payne (2017, their Figure 7).…”

“…The general aim of EOF analysis is to efficiently extract the most dominant modes of variability from large data sets by decomposing the associated space-time field into spatial patterns and time indices, or principal components (Wilks, 2006). This analysis has been demonstrated to be skillful in capturing the essential dynamics of the subpolar gyre (SPG), which is now recognized to have significant implications for a wide range of climatic (Lohmann et al, 2009a), and ecological (Hátún, Payne, Beaugrand, et al, 2009;Hátún, Payne, & Jacobsen, 2009;Hátún et al, 2016;Hátún, Azetsu-Scott, et al, 2017;Hátún, Olsen, et al, 2017;Hovland et al, 2013;Solmundsson et al, 2010) aspects of the North Atlantic Ocean.…”

“…Our investigation reveals that this confusion likely originates from the utilization of different satellite altimetry products, from the inclusion of different time periods and domains of the North Atlantic Ocean in publicized analyses. These studies have consequently led to different characteristics of the gyre index and therefore contradictory interpretations of the gyre-associated dynamics (Berx & Payne, 2017;Foukal & Lozier, 2017;Hátún, Olsen, et al, 2017). For example, some researchers have tied the index to the rotation intensity of the SPG (Foukal & Lozier, 2017;Lohmann et al, 2009b), while others focus on the size or the shape of the SPG (Hátún et al, 2016).…”

“…Thus, the gyre index depends on the altimetry data source, the chosen spatial domain, and whether any normalization has been applied. Recent studies have spatially limited the analysis to the SPG domain, but despite this spatial focus, the first principal components based on the new DUACS DT2014 (Berx & Payne, 2017;Hátún, Olsen, et al, 2017) are still more dominated by a long-term linear trend than is evident in the previous index presented by, for example, Larsen et al (2012). We also note that the number of years included in the EOF analysis influences the PCs (not shown)-for example, an analysis based on the shorter 1993-2004 period results in a PC1 with a steeper post-1995 trend than apparent in Figure 1b.…”

“…A principal reason for the present confusion in the literature is that the new publications (Berx & Payne, 2017;Foukal & Lozier, 2017;Hátún, Olsen, et al, 2017) rigidly treat PC1 as the gyre index. Many of the concerns expressed by Foukal and Lozier (2017) are rooted in this mistake.…”