scholarly journals Flexibility in Antarctic krill Euphausia superba decouples diet and recruitment from overwinter sea-ice conditions in the northern Antarctic Peninsula

2020 ◽  
Vol 642 ◽  
pp. 1-19 ◽  
Author(s):  
J Walsh ◽  
CS Reiss ◽  
GM Watters
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Antarctic Peninsula ◽  
Lipid Content ◽  
Environmental Variables ◽  
Antarctic Krill ◽  
Euphausia Superba ◽  
Ice Cover ◽  
Ice Conditions ◽  
Ice Resources

Winter sea-ice conditions are considered important for Antarctic krill Euphausia superba survival and recruitment, yet few broad-scale longitudinal studies have examined the underlying relationships between winter conditions and krill recruitment. We used data from a 4 yr winter study of krill condition (lipid content), diet (stable isotopes and fatty acids), and length distributions around the northern Antarctic Peninsula to examine relationships among environmental variables (annual sea-ice cover, water column chlorophyll a [chl a], and upper mixed-layer water temperature), the condition and diet of krill, and recruitment success the following year. Diet indicators (lipid content, δ15N, δ13C, and the fatty acid ratios 16:1n-7/18:4n-3 and 18:1n-9/18:1n-7) in post-larvae were consistent among years regardless of sea-ice cover, suggesting that post-larval krill do not rely on sea-ice resources for overwinter survival. Diet indicators in larvae were more variable and suggest that larvae may feed on sea-ice resources when they are available but can still persist in the water column when they are not. Principal component analysis between environmental variables and diet indicators showed that water-column chl a was the only variable that significantly affected diet, regardless of annual changes in sea-ice cover. Extensive winter ice in one year did not translate into successful recruitment the following year. Krill demonstrate a high degree of flexibility with respect to overwinter habitat and diet, and the degree to which sea ice is important during different times of year and at different life stages may be more complex than previously thought.

scholarly journals Sea-ice habitat minimizes grazing impact and predation risk for larval Antarctic krill

Polar Biology ◽  
2021 ◽  
Author(s):  
Carmen L. David ◽  
Fokje L. Schaafsma ◽  
Jan A. van Franeker ◽  
Evgeny A. Pakhomov ◽  
Brian P. V. Hunt ◽  
...  
Keyword(s):  
Sea Ice ◽  
Predation Risk ◽  
Water Column ◽  
Antarctic Krill ◽  
Standing Stock ◽  
Euphausia Superba ◽  
Grazing Impact ◽  
Water Interface ◽  
Winter Habitat ◽  
Ice Water

AbstractSurvival of larval Antarctic krill (Euphausia superba) during winter is largely dependent upon the presence of sea ice as it provides an important source of food and shelter. We hypothesized that sea ice provides additional benefits because it hosts fewer competitors and provides reduced predation risk for krill larvae than the water column. To test our hypothesis, zooplankton were sampled in the Weddell-Scotia Confluence Zone at the ice-water interface (0–2 m) and in the water column (0–500 m) during August–October 2013. Grazing by mesozooplankton, expressed as a percentage of the phytoplankton standing stock, was higher in the water column (1.97 ± 1.84%) than at the ice-water interface (0.08 ± 0.09%), due to a high abundance of pelagic copepods. Predation risk by carnivorous macrozooplankton, expressed as a percentage of the mesozooplankton standing stock, was significantly lower at the ice-water interface (0.83 ± 0.57%; main predators amphipods, siphonophores and ctenophores) than in the water column (4.72 ± 5.85%; main predators chaetognaths and medusae). These results emphasize the important role of sea ice as a suitable winter habitat for larval krill with fewer competitors and lower predation risk. These benefits should be taken into account when considering the response of Antarctic krill to projected declines in sea ice. Whether reduced sea-ice algal production may be compensated for by increased water column production remains unclear, but the shelter provided by sea ice would be significantly reduced or disappear, thus increasing the predation risk on krill larvae.

Multiproxy climate and sea ice reconstruction of the industrial era at the Western Antarctic Peninsula

2020 ◽  
Author(s):  
Maria-Elena Vorrath ◽  
Paola Cárdenas ◽  
Lorena Rebolledo ◽  
Xiaoxu Shi ◽  
Juliane Müller ◽  
...  
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
System Analysis ◽  
Ice Cover ◽  
Weddell Sea ◽  
Water Masses ◽  
Western Antarctic Peninsula ◽  
Climate Conditions ◽  
Ice Conditions ◽  
Bransfield Basin

<p>Recent changes and variability in climate conditions leave a significant footprint on the distribution and properties of sea ice, as it is sensitive to environmental variations. We investigate the rapidly transforming region of the Western Antarctic Peninsula (WAP) focusing on the conditions and development of sea ice in the pre-satellite era. For this study on past sea ice cover we apply the novel proxy IPSO<sub>25</sub> (Ice Proxy for the Southern Ocean with 25 carbon atoms; Belt et al., 2016). Three sampling sites were selected to cover areas near the Antarctic mainland, in the Bransfield Basin (2000 m depth) and the deeper shelf under an oceanographic frontal system. Analysis of short cores (multicores) resolving the last 200 years (based on <sup>210</sup>Pb<sub>ex</sub> dating) focused on geochemical bulk parameters, biomarkers (highly branched isoprenoids, GDGTs, sterols) and diatoms. These results are compared to multiple climate archives and modelled data. This multiproxy based approach provides insights on changes in spring sea ice cover, primary production regimes, subsurface ocean temperature (SOT based on TEX<sup>L</sup><sub>86</sub>) and oceanographic as well as atmospheric circulation patterns. While environmental proxies preserved in two cores near the coast and in the Bransfield Basin reflect the properties of water masses from the Bellingshausen Sea and Weddell Sea, respectively, data from the third core at the deeper shelf depict mixed signals of both water masses. Our study reveals clear evidence for warm and cold periods matching with ice core records and other marine sediment data at the WAP. We observe a general decrease in SOT and an increase in sea ice cover overprinted by high decadal fluctuations. Trends in SOT seem to be decoupled from atmospheric temperatures in the 20<sup>th</sup> century, and this is supported by previous studies (e.g. Barbara et al., 2013), and may be related to the Southern Annual Mode. We consider numerical modelling of sea ice conditions, sea surface temperature and SOT for further support of our findings.</p><p> </p><p>References:</p><p>Barbara, L., Crosta, X., Schmidt, S. and Massé, G.: Diatoms and biomarkers evidence for major changes in sea ice conditions prior the instrumental period in Antarctic Peninsula, Quat. Sci. Rev., 79, 99–110, doi:10.1016/j.quascirev.2013.07.021, 2013.</p><p>Belt, S. T., Smik, L., Brown, T. A., Kim, J. H., Rowland, S. J., Allen, C. S., Gal, J. K., Shin, K. H., Lee, J. I. and Taylor, K. W. R.: Source identification and distribution reveals the potential of the geochemical Antarctic sea ice proxy IPSO25, Nat. Commun., 7, 1–10, doi:10.1038/ncomms12655, 2016.</p>

scholarly journals Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by changes in insolation and ENSO variability

2013 ◽  
Vol 9 (4) ◽  
pp. 1431-1446 ◽  
Author(s):  
J. Etourneau ◽  
L. G. Collins ◽  
V. Willmott ◽  
J.-H. Kim ◽  
L. Barbara ◽  
...  
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Antarctic Peninsula ◽  
Primary Productivity ◽  
Climatic Factors ◽  
Southern Oscillation ◽  
Western Antarctic Peninsula ◽  
Deep Basin ◽  
Sea Ice Extent ◽  
Ice Conditions

Abstract. The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0–200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep Basin. Employing a multi-proxy approach, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEX86L for temperature) and micropaleontological data (diatom assemblages), we derived new Holocene records of sea ice conditions and upper water column temperatures. The early Holocene (9000–7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~7000–3800 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~2100 yr) was characterized by warmer temperatures and increased sea ice presence, accompanied by reduced local primary productivity, likely in response to a shorter growing season compared to the early or mid-Holocene. The gradual increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation, despite increasing summer insolation. We postulate that, in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of the El Niño–Southern Oscillation (ENSO). However, between 3800 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time.

scholarly journals Holocene climate variations in the western Antarctic Peninsula: evidence for sea ice extent predominantly controlled by insolation and ENSO variability changes

2013 ◽  
Vol 9 (1) ◽  
pp. 1-41 ◽  
Author(s):  
J. Etourneau ◽  
L. G. Collins ◽  
V. Willmott ◽  
J. H. Kim ◽  
L. Barbara ◽  
...  
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Antarctic Peninsula ◽  
Primary Productivity ◽  
Climatic Factors ◽  
Southern Oscillation ◽  
Western Antarctic Peninsula ◽  
Deep Basin ◽  
Sea Ice Extent ◽  
Ice Conditions

Abstract. The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatures (0–200 m) and primary productivity over the last 9000 yr BP (before present) in the western Antarctic Peninsula (WAP) margin from a sedimentary core collected in the Palmer Deep basin. Employing a multi-proxy approach, we derived new Holocene records of sea ice conditions and upper water column temperatures, based on the combination of two biomarkers proxies (highly branched isoprenoid (HBI) alkenes for sea ice and TEXL86 for temperature) and micropaleontological data (diatom assemblages). The early Holocene (9000–7000 yr BP) was characterized by a cooling phase with a short sea ice season. During the mid-Holocene (~ 7000–3000 yr BP), local climate evolved towards slightly colder conditions and a prominent extension of the sea ice season occurred, promoting a favorable environment for intensive diatom growth. The late Holocene (the last ~ 3000 yr) was characterized by more variable temperatures and increased sea ice presence, accompanied by reduced local primary productivity likely in response to a shorter growing season compared to the early or mid-Holocene. The stepwise increase in annual sea ice duration over the last 7000 yr might have been influenced by decreasing mean annual and spring insolation despite an increasing summer insolation. We postulate that in addition to precessional changes in insolation, seasonal variability, via changes in the strength of the circumpolar Westerlies and upwelling activity, was further amplified by the increasing frequency/amplitude of El Niño-Southern Oscillation (ENSO). However, between 4000 and 2100 yr BP, the lack of correlation between ENSO and climate variability in the WAP suggests that other climatic factors might have been more important in controlling WAP climate at this time.

scholarly journals Highly branched isoprenoids for Southern Ocean semi-quantitative sea ice reconstructions: a pilot study from the Western Antarctic Peninsula

2019 ◽  
Author(s):  
Maria-Elena Vorrath ◽  
Juliane Müller ◽  
Oliver Esper ◽  
Gesine Mollenhauer ◽  
Christian Haas ◽  
...  
Keyword(s):  
Sea Ice ◽  
Antarctic Peninsula ◽  
Environmental Changes ◽  
Transfer Functions ◽  
Drake Passage ◽  
Ice Cover ◽  
Time Intervals ◽  
Ice Conditions ◽  
Instrumental Records ◽  
Diatom Transfer Functions

Abstract. Organic geochemical and micropaleontological analyses of surface sediments collected in the southern Drake Passage and the Bransfield Strait, Antarctic Peninsula, enable a proxy-based reconstruction of recent sea ice conditions in this climate sensitive area. The distribution of the sea ice biomarker IPSO25 supports earlier suggestions that the source diatoms seem to be common in near-coastal environments characterized by an annually recurring sea ice cover. We here propose and evaluate the combination of IPSO25 with a more unsaturated highly branched isoprenoid alkene and phytosterols and introduce the PIPSO25 index as a potentially semi-quantitative sea ice proxy. This organic geochemical approach is complemented with diatom data. PIPSO25 sea ice estimates are used to discriminate between areas characterized by permanently ice-free conditions, seasonal sea ice cover and extended sea ice cover. These trends are consistent with satellite sea ice data and winter sea ice concentrations estimated by diatom transfer functions. Minor offsets between proxy-based and satellite-based sea ice data are attributed to the different time intervals recorded within the sediments and the instrumental records from the study area, which experienced rapid environmental changes during the past 100 years.

Effects of sea ice cover on the swarming behaviour of Antarctic krill, Euphausia superba

2000 ◽  
Vol 57 (S3) ◽  
pp. 24-30 ◽  
Author(s):  
Andrew S Brierley ◽  
Jonathan L Watkins
Keyword(s):  
Sea Ice ◽  
Antarctic Krill ◽  
Open Water ◽  
Euphausia Superba ◽  
Ice Cover ◽  
Sea Ice Extent ◽  
Neighbour Distance ◽  
Bellingshausen Sea ◽  
Antarctic Krill Euphausia Superba ◽  
Swarming Behaviour

Much of the distribution range of Antarctic krill, Euphausia superba, is covered by permanent or seasonal sea ice. Sea ice extent has been implicated as a major factor affecting reproductive success of krill and krill dispersal, but little is known of the way in which ice cover may influence krill behaviour. This is largely because the under-ice environment is difficult to study. Ship-borne echosounders have, however, detected krill aggregations in midwater in ice-covered regions. We used 120-kHz echograms collected underway during three cruises that crossed ice-covered and adjacent open waters in the Bellingshausen, Weddell, and Scotia seas to compare morphological and next-neighbour characteristics of krill swarms within and without ice cover. No significant differences were detected between the horizontal and vertical extent of swarms or swarm next-neighbour distance in ice-covered or open waters. Distributions of swarm mid-depths did, however, differ significantly between ice-covered and open areas in all three seas, although the direction of difference was not the same in each instance: swarms in the Weddell and Scotia seas were generally shallower under ice than in open water, whereas in the Bellingshausen Sea the opposite prevailed.

Length and age at maturity of Antarctic krill

1994 ◽  
Vol 6 (4) ◽  
pp. 479-482 ◽  
Author(s):  
V. Siegel ◽  
V. Loeb
Keyword(s):  
Antarctic Peninsula ◽  
Sexual Maturity ◽  
Antarctic Krill ◽  
Euphausia Superba ◽  
Knife Edge ◽  
Age At Maturity ◽  
Growth Season ◽  
The Third ◽  
Age Class ◽  
The Antarctic

Data from several summer research cruises in the Antarctic Peninsula region were analysed to calculate length (L50) and age at maturity for the Antarctic krill, Euphausia superba. Length at maturity L50 is defined as the length at which 50% of the krill stock attains sexual maturity. L50 values of 34.65–35.91 mm for female krill are the best estimates for the peak spawning season. Males attain sexual maturity later at L50 values of 43.35–43.71 mm. Length at maturity and length at first spawning are identical for krill. Comparisons with mean length-at-age data show that females mature in the third growth season (age class 2+), while males reach maturity in the fourth year (age class 3+). Both sexes show ‘knife-edge maturity’.

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