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John W Durban - One of the best experts on this subject based on the ideXlab platform.
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cooperative hunting behavior prey selectivity and prey handling by Pack Ice killer whales orcinus orca type b in antarctic peninsula waters
Marine Mammal Science, 2012Co-Authors: Robert L. Pitman, John W DurbanAbstract:Currently, there are three recognized ecotypes (or species) of killer whales (Orcinus orca) in Antarctic waters, including type B, a putative prey specialist on seals, which we refer to as “Pack Ice killer whale” (PI killer whale). During January 2009, we spent a total of 75.4 h observing three different groups of PI killer whales hunting off the western Antarctic Peninsula. Observed prey taken included 16 seals and 1 Antarctic minke whale (Balaenoptera bonaerensis). Weddell seals (Leptonychotes weddellii) were taken almost exclusively (14/15 identified seal kills), despite the fact thattheyrepresentedonly15%of365sealsidentifiedonIcefloes;thewhalesentirely avoided taking crabeater seals (Lobodon carcinophaga; 82% relative abundance) and leopard seals (Hydrurga leptonyx; 3%). Of the seals killed, the whales took 12/14 (86%) off Ice floes using a cooperative wave-washing behavior; they produced 120 waves during 22 separate attacks and successfully took 12/16 (75%) of the Weddell seals attacked. The mean number of waves produced per successful attack was 4.1 (range 1–10) and the mean attack duration was 30.4 min (range 15–62). Seal remains that we examined from one of the kills provided evidence of meticulous postmortem prey processing perhaps best termed “butchering.”
A P Worby - One of the best experts on this subject based on the ideXlab platform.
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regional scale sea Ice and snow thickness distributions from in situ and satellite measurements over east antarctica during sipex 2007
Deep-sea Research Part Ii-topical Studies in Oceanography, 2011Co-Authors: Ian Allison, Ad Steer, A P Worby, J L Lieser, Petra Heil, Thorsten MarkusAbstract:The Sea Ice Physics and Ecosystem eXperiment (SIPEX) was conducted in the East Antarctic Pack Ice zone between 115-130 degrees E from 9 September - 11 October, 2007. In situ measurements of sea-Ice and snow properties were conducted at 15 Ice stations, together with ship-based ASPeCt observations. The Ice and snow thickness varied considerably in different regions of the Pack Ice, with particularly thick Ice associated with deformation and a strong slope jet in the southwest of the study region. The mean Ice thickness was 0.99 m (1.57 m excluding the northern marginal Ice zones), but varied from 0.61 m along the southern leg to 1.80 m along the western leg, with pockets of considerably thicker Ice in some regions. Swell was observed on two occasions penetrating more than 330 km south of the Ice edge into regions with 80-100% Ice concentration. Ice thicknesses calculated from near coincident IceSat laser altimetry (1.74 m) are similar to the in-situ observations in the central Pack (1.57 m). (C) 2010 Elsevier Ltd. All rights reserved.
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determining the floe size distribution of east antarctic sea Ice from digital aerial photographs
Annals of Glaciology, 2001Co-Authors: M J Paget, A P Worby, K J MichaelAbstract:Floe size within the Antarctic Pack Ice is an important parameter that affects both the ocean-Ice-atmosphere energy exchange and the mechanical properties of Pack Ice. In this paper we present a computer-based algorithm to extract floe-size distribution information from digital aerial photographs of Antarctic sea Ice. The algorithm segments digital images of sea Ice into distinct floes from which the size of each floe is calculated and floe-size distributions are derived. Through a recursive application of the morphological erosion operator, each floe is eroded towards its centre while each pixel’s erosion number is recorded. This ensures no information is lost while individual floes are identified. The algorithm combines image-processing techniques with some manual input to accurately identify the boundaries of individual floes within an image. To demonstrate the functionality of the algorithm, six images, representing regions along a 22 km south-to-north transect through a transitional zone of Pack Ice near 65° S, 140° E, have been processed. Regional variations in the floe-size distributions show an increase in the number of smaller floes relative to larger floes and a decrease in the dominant floe size (in terms of areal coverage) from south to north. These results are consistent with ship-based observations.
G C Cripps - One of the best experts on this subject based on the ideXlab platform.
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changes in lipid composition of copepods and euphausia superba associated with diet and environmental conditions in the marginal Ice zone bellingshausen sea antarctica
Deep Sea Research, 1998Co-Authors: G C Cripps, H J HillAbstract:The effect of varying diet and environmental conditions at the Marginal Ice Zone (MIZ) on the fatty acid and hydrocarbon compositions of five species of copepod and krill, Euphausia superba, was investigated. Zooplankton at the MIZ experienced a range of conditions, from a low algal biomass (mainly flagellates) under Pack-Ice to a spring bloom dominated by diatoms in the open ocean. Principal Component Analysis classified the copepods into three dietary regimes: (i) omnivores or general algal feeders under the Pack Ice, (ii) dinoflagellate feeders, and (iii) diatom feeders in the open ocean. This classification was supported by the distribution of the diatom marker n-heneicosahexaene (n-C21:6) and a general indicator of herbivory, the isoprenoid pristane. The fatty acid and hydrocarbon composition reflected dietary preferences and availability as the season progressed. Of the copepods under the Pack-Ice, Oithona spp. was omnivorous whereas Calanus propinquus was feeding preferentially on flagellates. Metridia gerlachei fed on flagellates in all conditions, but also included diatoms in its diet during the bloom. Calanoides acutus and Rhincalanus gigas, which passed the winter in diapause, were feeding almost exclusively on diatoms in the open ocean. Euphausia superba, which were also mainly diatom feeders in the open ocean, were feeding on the sea-Ice algae (diatoms) and suspended material from the water column (dinoflagellates) under the Pack-Ice.
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biogenic hydrocarbons in the particulate material of the water column of the bellingshausen sea antarctica in the region of the marginal Ice zone
Deep-sea Research Part Ii-topical Studies in Oceanography, 1995Co-Authors: G C CrippsAbstract:The biogenic hydrocarbon content of particulate matter of the Bellingshausen Sea in the region of the marginal Ice zone (MIZ) has been used to investigate the origins and fates of organic material in the water column in the region of a marginal Ice zone. Particulates were sampled from four depths to 200 m in Pack Ice and at the Ice edge, and from seven depths to 3000 m in open ocean. Total n-alkane concentrations associated with particulates increased from 200 ng l−1 under the Pack Ice to 1000 ng l−1 in the open ocean, and decreased with depth in open water to 15 ng l−1 at 3000 m. The influence of phytoplankton on particulate material was shown to be negligible under the Ice but extended horizontally and vertically as the Ice edge retreated. Sea-Ice algae did not appear to seed the phytoplankton growth under the Ice or the subsequent “bloom” at the MIZ. The alkane signature of phytoplankton from the MIZ bloom was detected at a depth of 200 m near the Ice edge, at 500 m in open sea, and in surface sediments (4100 m). Zooplankton biomarkers that were at low levels in krill under the Ice were higher in animals from the open ocean but were not detected in the water column or sediments. It was concluded that the majority of particulate material in the water column was algal in origin. Material in the surface sediment from under Pack Ice probably originated from a deep-living winter population of copepods and material in surface sediment from the Ice-free ocean originated from the algal “bloom” at the MIZ.
Ian Allison - One of the best experts on this subject based on the ideXlab platform.
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regional scale sea Ice and snow thickness distributions from in situ and satellite measurements over east antarctica during sipex 2007
Deep-sea Research Part Ii-topical Studies in Oceanography, 2011Co-Authors: Ian Allison, Ad Steer, A P Worby, J L Lieser, Petra Heil, Thorsten MarkusAbstract:The Sea Ice Physics and Ecosystem eXperiment (SIPEX) was conducted in the East Antarctic Pack Ice zone between 115-130 degrees E from 9 September - 11 October, 2007. In situ measurements of sea-Ice and snow properties were conducted at 15 Ice stations, together with ship-based ASPeCt observations. The Ice and snow thickness varied considerably in different regions of the Pack Ice, with particularly thick Ice associated with deformation and a strong slope jet in the southwest of the study region. The mean Ice thickness was 0.99 m (1.57 m excluding the northern marginal Ice zones), but varied from 0.61 m along the southern leg to 1.80 m along the western leg, with pockets of considerably thicker Ice in some regions. Swell was observed on two occasions penetrating more than 330 km south of the Ice edge into regions with 80-100% Ice concentration. Ice thicknesses calculated from near coincident IceSat laser altimetry (1.74 m) are similar to the in-situ observations in the central Pack (1.57 m). (C) 2010 Elsevier Ltd. All rights reserved.
Robert L. Pitman - One of the best experts on this subject based on the ideXlab platform.
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cooperative hunting behavior prey selectivity and prey handling by Pack Ice killer whales orcinus orca type b in antarctic peninsula waters
Marine Mammal Science, 2012Co-Authors: Robert L. Pitman, John W DurbanAbstract:Currently, there are three recognized ecotypes (or species) of killer whales (Orcinus orca) in Antarctic waters, including type B, a putative prey specialist on seals, which we refer to as “Pack Ice killer whale” (PI killer whale). During January 2009, we spent a total of 75.4 h observing three different groups of PI killer whales hunting off the western Antarctic Peninsula. Observed prey taken included 16 seals and 1 Antarctic minke whale (Balaenoptera bonaerensis). Weddell seals (Leptonychotes weddellii) were taken almost exclusively (14/15 identified seal kills), despite the fact thattheyrepresentedonly15%of365sealsidentifiedonIcefloes;thewhalesentirely avoided taking crabeater seals (Lobodon carcinophaga; 82% relative abundance) and leopard seals (Hydrurga leptonyx; 3%). Of the seals killed, the whales took 12/14 (86%) off Ice floes using a cooperative wave-washing behavior; they produced 120 waves during 22 separate attacks and successfully took 12/16 (75%) of the Weddell seals attacked. The mean number of waves produced per successful attack was 4.1 (range 1–10) and the mean attack duration was 30.4 min (range 15–62). Seal remains that we examined from one of the kills provided evidence of meticulous postmortem prey processing perhaps best termed “butchering.”
