Temporal changes in euphausiid distribution and abundance in North Atlantic cold-core rings in relation to the surrounding waters
Figure 1: Vertical profiles of temperature at the center of cold-core rings of various ages (months): Bob at 1 and 5 months old, Al at 2.5 months old, D at 6 and 9 months old, Franklin at 7 months old, and Emerson at 12 months old (911.9Kb)
Figure 2: Relationship between ring age (months) and the mean temperature in the upper 700 m (°C) and depth of 15°C isotherm (m) (502.4Kb)
Figure 3: Abundance of each euphausiid species in cold-core rings of 1 (a), 5 (b), 6 (c), 7 (d), 9 (e) and 12 (e) months old (550.6Kb)
Figure 6: Number of species that occurred and Pielou’s J’ in cold-core rings of various ages (a); seasonal change in these values in the Slope Water (b); and in the northern Sargasso Sea (c) (544.6Kb)
Figure 7: Change in abundance of total euphausiids (a), cold-water species (b), warm-water species (c), wide-ranging warm-water species (d), transition species, Thysanoessa gregaria (e), and Thysanoessa parva (f) with ring age (571.6Kb)
Figure 8: Change in percentage of cold-water species, warm-water species, wide-ranging warm-water species, transition species (Thysanoessa gregaria), and Thysanoessa parva to the total euphausiid population with ring age (465.4Kb)
Figure 9: Relationship between the percentage of cold-water species (left) and warm-water species (right) and ring age (497.3Kb)
Figure 10: Results of nonmetric MDS based on euphausiid species composition in 139 tows made in northwestern North Atlantic (a) (535.1Kb)
Figure 11: Abundance of cold-water (left) and warm-water (right) species plotted on the coordinates of nonmetric MDS (553.6Kb)
Figure 12: ertical distribution of total euphausiid species (a), cold-water species (b), and warm-water species (c) during the day and at night at the center of cold-core rings of various ages (months) (850.4Kb)
Figure 13: Vertical distribution of Euphausia krohni (a), Nematoscelis megalops (b), E. brevis (c), and Stylocheiron carinatum (d) during the day and at night at the center of cold-core rings of various ages (months) (840.9Kb)
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The species composition of euphausiids was investigated in relationship to the hydrographic conditions in the North Atlantic cold-core rings (CCR) and adjacent waters to elucidate species succession in evolving water masses. Using data, dating back to the 1970’s, from as many CCRs as possible and selecting typical cases where no major physical perturbations occurred, a general pattern of euphausiid succession and change in vertical distribution in rings with time was obtained. This pattern was related to the general distribution of euphausiids in the northwestern North Atlantic Ocean, aiming at providing basic information on probable response of North Atlantic marine ecosystem to global warming. Of the 34 euphausiid species identified, 5 were cold-water species, 17 were warm-water species, 6 were wide-ranging warm-water species, 1 was transitional, 4 were cosmopolitan and the remaining was Thysanoessa parva. Among cold-water species, Euphausia krohni and Nematoscelis megalops were dominant in CCRs. E. krohni became rare in rings older than 6 months, whereas N. megalops survived longer, being abundant in some rings of 9 months or older, by staying within its preferred temperature range as the CCR elevated isotherms sank to depths where they are normally found in the Sargasso Sea and because it is an omnivore-carnivore. Among warm-water species, epipelagic species appeared first in rings, corresponding to the physical change occurring most rapidly in the surface layers. Mesopelagic species appeared later. Cold-water species made up 65-85% of the total euphausiid population in number in younger rings (1-5 months old), while warm-water species contributed only 2-7%. Wide-ranging warm-water species made up about up to one fourth of the total in rings 5 and 7 months old. Warm-water species, mainly E. brevis, increased in older rings (9 months old or older) and made up 50% of the total in the oldest ring. The contribution of cold-water species decreased to 14% in older rings. T. parva made up 26-38% of the total in rings 6 months or older. CCR populations can be characterized by high species number, but intermediate evenness between the Slope Water and northern Sargasso Sea. In CCRs, only a limited number of species were dominant even if there were more species present in rings as old as 9-12 months than in the northern Sargasso Sea. In rings older than 9 months, euphausiids showed two peaks in their vertical distribution: a shallow daytime peak at about 400 m and a nighttime peak in the upper 100 m consisting of warm-water species (mainly E. brevis) and a deeper persistent peak at 800 m or deeper consisting of the species N. megalops and T. parva. This shallow peak in CCRs is shallower than that in the surrounding northern Sargasso Sea, and the deep peak is rarely observed in these waters.
Author Posting. © Elsevier B.V., 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part I: Oceanographic Research Papers 54 (2007): 181-202, doi:10.1016/j.dsr.2006.10.008.
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