Impact of the climate regime shift around 2000 on recruitment of Antarctic krill at the Antarctic Peninsula and South Georgia

Abstract

We examined how the climate regime shift around 2000 affected Antarctic krill recruitment variability at the North Antarctic Peninsula (NAP) and South Georgia (SG) during the period of 1990s through to 2000s. We used sea surface temperature (SST) as a proxy of the monthly sea ice extent and related it to the recruitment index (proportion of 1-year-old krill) of each succeeding year for NAP and SG by examining the correlation of the time series before and after 2000. For NAP, recruitment index was negatively correlated with winter SST at NAP in the 1990s but with autumn SST in the 2000s, suggesting that good recruitment was supported by extensive winter sea-ice in the 1990s but by extensive autumn sea-ice in the 2000s. This was attributed to the regime shift featured by winter warming and autumn cooling after 2000. For SG, recruitment was negatively correlated with winter SST at NAP in the 1990s but positively correlated with autumn SST in the southern Scotia Sea (SSS) in the 2000s. According to particle tracking experiment from NAP to SG in relation to the sea-ice extent and position of SACCF (Southern Antarctic Circumpolar Current Front), less sea-ice extent in 2000s meant less larvae distributing as north as SACCF, resulting in much fewer larval being transported to SG. Hence, we hypothesized that the regime shift weakened the connection between NAP and SG, but instead SSS became the main driver of recruitment at SG. We presume the krill population demonstrated adaptability to the regime shift by offsetting the unfavorable winter condition with the favorable autumn condition at NAP and for SG, replacing the source of recruits with those closer to it.