What happened to gray whales during the pleistocene? the ecological impact of sea-level change on benthic feeding areas in the north pacific ocean

PLoS ONE

Volumn 6, Issue 7, 2011, Pages

  Pyenson, Nicholas D ^a,b   Lindberg, David R ^c  

^a DEPARTMENT OF PALEOBIOLOGY   (United States)

^b UNIVERSITY OF WASHINGTON   (United States)

^c UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; BENTHOS; ENVIRONMENTAL CARRYING CAPACITY; ENVIRONMENTAL IMPACT; FEEDING; FEEDING ECOLOGY; GLACIATION; GRAY WHALE; PACIFIC OCEAN; PLEISTOCENE; POPULATION SIZE; QUANTITATIVE ANALYSIS; SEA LEVEL; WHALE; ANIMAL; FEEDING BEHAVIOR; ICE COVER; PHYSIOLOGY; POPULATION MIGRATION; TIME;

ESCHRICHTIIDAE; ESCHRICHTIUS ROBUSTUS; INVERTEBRATA;

SEA WATER;

ANIMAL MIGRATION; ANIMALS; FEEDING BEHAVIOR; ICE COVER; PACIFIC OCEAN; SEAWATER; TIME FACTORS; WHALES;

EID: 79960011115     PISSN: None     EISSN: 19326203     Source Type: Journal    
DOI: 10.1371/journal.pone.0021295     Document Type: Article

References (115)

1. Martin PS, Klein RG, (1984) Quaternary extinctions: a prehistoric revolution Tucson University of Arizona Press.
2. Koch PL, Barnosky AD, (2006) Late Quaternary extinctions: state of the debate. Ann Rev Ecol Evol Syst 37: 215-250.
3. Barnosky AD, Koch PL, Feranec RS, Wing SL, Shabel AB, (2004) Assessing the Causes of Late Pleistocene Extinctions on the Continents. Science 306: 70-75.
4. Gill JL, Williams JW, Jackson ST, Lininger KB, Robinson GS, (2009) Pleistocene megafaunal collapse, novel plant communities, and enhanced fire regimes in North America. Science 326: 1100-1103.
5. Domning DP, (1978) Sirenian evolution in the North Pacific Ocean. Univ Calif Pub Geol Sci 118: 1-176.
6. LeBoeuf BJ, Kenyon KW, Villa-Ramirez B, (1986) The Caribbean monk seal is extinct. Mar Mamm Sci 2: 70-72.
7. Anderson PK, (2001) Marine mammals in the next one hundred years: twilight for a Pleistocene megafauna? J Mamm 82: 623-629.
8. Turvey ST, Pitman RL, Taylor BL, Barlow J, Akamatsu T, et al. (2007) First human-caused extinction of a cetacean species? Biology Letters 3: 537-540.
9. Rick TC, Erlandson JM, Vellanoweth RL, Braje TJ, (2005) From Pleistocene mariners to complex hunter-gatherers: The archaeology of the California Channel Islands. Journal of World Prehistory 19: 169-22.
10. Newsome SD, Etnier MA, Gifford-Gonzalez D, Phillips DL, van Tuinen M, et al. (2007) The shifting baseline of northern fur seal (Callorhinus ursinus) ecology in the northeast Pacific Ocean. Proc Natl Acad Sci U S A 104: 9709-9714.
11. Stringer C, Finlayson JC, Barton RNE, Fernández-Jalvo Y, Cáceres I, et al. (2008) Neanderthal exploitation of marine mammals in Gibraltar. Proc Natl Acad Sci U S A 105: 14319-14324.
12. Jackson JBC, (2006) When ecological pyramids were upside down. In: Estes JA, DeMaster DP, Doak DF, Williams TM, Brownell BL, editors. Whales, whaling and ocean ecosystems Berkeley University of California Press pp. 27-37.
13. Schipper J, Chanson JS, Chiozza F, Cox NA, Hoffman M, et al. (2008) The status of the world's land and marine mammals: diversity, threat, and knowledge. Science 322: 225-230.
14. Roman J, Palumbi SR, (2003) Whales before whaling in the North Atlantic. Science 301: 508-510.
15. Alter SE, Rynes E, Palumbi SR, (2007) DNA evidence for historic population size and past ecosystem impacts of gray whales. Proc Natl Acad Sci U S A 104: 15162-15167.
16. Alter SE, Palumbi SR, (2007) Could genetic diversity in eastern North Pacific gray whales reflect global historic abundance? Proc Natl Acad Sci U S A 104: E3.
17. Mead JG, Mitchell ED, (1984) Atlantic gray whales. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 33-53.
18. Bryant PJ, (1995) Dating remains of gray whales from the Eastern North Atlantic. J Mamm 76: 857-861.
19. Lindquist O, (2000) The North Atlantic gray whale (Escherichtius [sic] robustus): An historical outline based on Icelandic, Danish-Icelandic, English and Swedish sources dating from ca 1000 AD to 1792. Occasional papers 1. Universities of St Andrews and Stirling, Scotland.
20. Bradford AL, Wade PR, Weller DW, Burdin AM, Ivashchenko YV, et al. (2006) Survival estimates of western gray whales Eschrichtius robustus incorporating individual heterogeneity and temporary emigration. Mar Ecol Prog Ser 315: 293-307.
21. Bradford AL, Weller DW, Wade PR, Burdin AM, Brownell RL Jr, (2008) Population abundance and growth rate of western gray whales Eschrichtius robustus. Endangered Species Res 16: 1-14.
22. Reilly SB, Bannister JL, Best PB, Brown M, Brownell RL Jr, (2010) Eschrichtius robustus (western subpopulation). In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4.Available: http://www.iucnredlist.org/apps/redlist/details/8099/0. Accessed 2010 Jun 8.
23. Rice DW, Wolman AA, (1971) The life history and ecology of the gray whale (Eschrichtius robustus). American Society of Mammalogists. Special Publication 3: 1-142.
24. Jones ML, Swartz SL, (1984) Demography and phenology of breeding gray whales in Laguna San Ignacio, Baja California Sur, Mexico: 1978 to 1982. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 309-374.
25. Scammon C, (1874) The marine mammals of the north-western coast of North America: together with an account of the American whale-fishery San Francisco John H. Carmany.
26. Nerini M, (1984) A review of gray whale feeding ecology. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 423-450.
27. Werth A, (2000) Feeding in marine mammals. In: Schwenk K, editors. Feeding: form, function and evolution in tetrapod vertebrates San Diego Academic Press pp. 487-526.
28. Sayers H, (1984) Shore whaling for gray whales along the coast of the Californias. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 121-157.
29. Henderson DA, (1984) Nineteenth century gray whaling: grounds, catches and kills, practices and depletion of the whale population. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 159-186.
30. Clapham PJ, Young SB, Brownell RL Jr, (1999) Baleen whales: Conservation issues and the status of the most endangered populations. Mamm Rev 29: 35-60.
31. Moore SE, Urban JR, Perryman WL, Gulland F, Perez-Cortez HM, et al. (2001) Are gray whales hitting "K" hard? Mar Mamm Sci 17: 954-958.
32. Wade PR, (2002) A Bayesian stock assessment of the eastern Pacific gray whale using abundance and harvest data from 1967 to 1996. J Cetacean Res Mgmt 4: 85-98.
33. Rugh DJ, Hobbs RC, Lerczak JA, Breiwick JM, (2005) Estimates of abundance of the eastern North Pacific stock of gray whales (Eschrichtius robustus) 1997-2002. J Cetacean Res Mgmt 7: 1-12.
34. Grebmeier JM, Overland JE, Moore SE, Farley EV, Carmack EC, et al. (2006) A major ecosystem shift in the northern Bering Sea. Science 311: 4161-4162.
35. Kim SL, Oliver JS, (1989) Swarming benthic crustaceans in the Bering and Chukchi seas and their relation to geographic patterns in gray whale feeding. Cdn J Zool 67: 1531-1542.
36. Moore SE, Grebmeier JM, Davies JR, (2003) Gray whale distribution relative to habitat in the northern Bering Sea: current conditions and retrospective summary. Cdn J Zool 81: 734-742.
37. Highsmith RC, Coyle KO, Bluhm BA, Konar B, (2006) Gray whales in the Bering and Chukchi Seas. In: Estes JA, DeMaster DP, Doak DF, Williams TM, Brownell BL, editors. Whales, Whaling and Ocean Ecosystems Berkeley University of California Press pp. 303-313.
38. National Research Council (1996) The Bering Sea Ecosystem Washington National Academy Press.
39. Tynan CT, (2004) Cetacean populations on the southeastern Bering Sea shelf during the late 1990s: Implications for decadal changes in ecosystem structure and carbon flow. Mar Ecol Prog Ser 272: 281-300.
40. Bringham-Grette J, (2001) New perspectives on Beringian Quaternary paleogeography, stratigraphy, and glacial history. Quat Sci Rev 20: 15-24.
41. Kaufman DS, Manley WF, (2004) Pleistocene Maximum and Late Wisconsin glacier extents across Alaska, U.S.A. In: Ehlers J, Gibbard PL, editors. pp. 9-27 Quaternary Glaciations: Extent and Chronology, Part II, North America: Developments in Quaternary Science 2b, Elsevier.
42. Takahashi K, (2005) The Bering Sea and paleoceanography. Deep Sea Res Part II: Topical Studies Oceanog 52: 2080-2091.
43. Miller KG, Kominz MA, Browning JV, Wright JD, Mountain GS, et al. (2005) The Phanerozoic record of global sea-level change. Science 310: 1293-1298.
44. Uhen MD, Pyenson ND, (2007) Diversity estimates, biases, and historiographic effects: resolving cetacean diversity in the Tertiary. Palaeontologia Electronica 10: 11A.
45. NOAA National Geophysical Data Center (2011) Bathymetry & Global Relief webpage. Available at http://www.ngdc.noaa.gov/mgg/bathymetry/relief.html. Accessed 2010 Jun 8.
46. Cacchione DA, Drake DE, Field ME, Tate GV, (1987) Seafloor gouges caused by migrating gray whales off northern California. Continental Shelf Res 7: 553-560.
47. Johnson KR, Nelson CH, (1984) Side-scan sonar assessments of gray whale feeding in the Bering Sea. Science 225: 1150-1152.
48. Calambokidis J, Darling JD, Deecke V, Gearin P, Gosho M, et al. (2002) Abundance, range and movements of a feeding aggregation of gray whales (Eschrichtius robustus) from California to southeastern Alaska in 1998. J Cetacean Res Mgmt 4: 267-276.
49. Palsbøll PJ, Bérubé M, Larsen F, (2007) Could genetic diversity in eastern North Pacific gray whales reflect global historic abundance? Proc Natl Acad Sci U S A 104: E2.
50. Barrett-Lennard LG, Matkin CO, Durban JW, Saulitis EL, Ellifrit D, (2011) Predation on gray whales and prolonged feeding on submerged carcasses by transient killer whales at Unimak Island, Alaska. Mar Ecol Prog Ser 421: 229-241.
51. Sancetta C, (1983) Effect of Pleistocene glaciation upon oceanographic characteristics of the North Pacific Ocean and Bering Sea. Deep Sea Res 30: 851-869.
52. Sancetta C, Heusser L, Labeyrie L, Naidu AS, Robinson SW, (1984) Wisconsin Holocene paleoenvironment of the Bering Sea-evidence from diatoms, pollen, oxygen isotopes and clay-minerals. Marine Geology 62: 55-68.
53. Sancetta C, (1992) Primary production in the glacial North Atlantic and North Pacific. Nature 360: 249-251.
54. Williams D, Dunkerley D, DeDeckker P, Kershaw P, Chappell M, (1998) Quaternary Environments London Arnold.
55. Bigg GR, Clark CD, Hughes ALC, (2008) A last glacial ice sheet on the Pacific Russian coast and catastrophic change arising from coupled ice-volcanic interaction. Earth and Planetary Sci Lett 265: 559-570.
56. Dearborn JH, (1963) Marine benthos at McMurdo Sound, Antarctica. Bull Ecol Soc Am 44: 41-42.
57. Dayton PK, Robilliard GA, De Vries AL, (1969) Anchor ice formation in McMurdo Sound, Antarctica, and its biological effects. Science 163: 273-274.
58. Dayton PK, Robilliard GA, Paine RT, Dayton LB, (1970) Biological accommodation in the benthic community at McMurdo Sound, Antarctica. Ecol Monogr 44: 105-128.
59. Kauffman TA, (1974) Seasonality and disturbance in benthic communities. Arthur Harbour, Antarctic Peninsula. Antarctic J U S 9: 307-310.
60. Berzin AA, (1984) Soviet studies of the distribution and numbers of the gray whale in the Bering and Chukchi Seas, from 1968-1982. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 409-419.
61. Stafford KM, Moore SE, Spillane M, Wiggins S, (2007) Gray whale calls recorded near Barrow, Alaska, throughout the Winter of 2003-04. Arctic 60: 167-172.
62. Grebmeier JM, McRoy CP, Feder HM, (1988) Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. I. Food supply source and benthic biomass. Mar Ecol Prog Ser 48: 57-67.
63. Grebmeier JM, Feder HM, McRoy CP, (1989) Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. II. Benthic community structure. Mar Ecol Prog Ser 51: 253-268.
64. Grebmeier JM, McRoy CP, (1989) Pelagic-benthic coupling on the shelf of the northern Bering and Chukchi Seas. III. Benthic food supply and carbon cycling. Mar Ecol Prog Ser 53: 79-91.
65. Scheinin AP, Kerema D, MacLeod CD, Gazoa M, Chicote CA, et al. (2011) Gray whale (Eschrichtius robustus) in the Mediterranean Sea: anomalous event or early sign of climate-driven distribution change? Marine Biodiversity Records 4: e28.
66. Noakes SE, Garrison E, McFall G, (2009) Underwater paleontology: recovery of a prehistoric whale mandible offshore Georgia. In: Pollock NW, editors. Diving for Science 2009 Proceedings of the American Academy of Underwater Sciences 28th Symposium, Atlanta, Georgia.
67. Weber DS, Stewart BS, Lehman N, (2003) Genetic consequences of a severe population bottleneck in the Guadalupe fur seal (Arctocephalus townsendi). J Heredity 95: 144-153.
68. Allendorf FW, England PR, Luikart G, Ritchie PA, Ryman N, (2008) Genetic effects of harvest on wild animal populations. TREE 23: 327-337.
69. Alter SE, Rosenbaum, (2009) The utility of historic samples in investigating the impacts of climate change on cetacean demography: bowhead and gray whales as case studies. International Marine Conservation Congress, George Mason University, Fairfax, Virginia, USA Arlington Kirby Lithographic.
70. ICUN (2011) Western gray whale makes unexpected journey. Available: http://www.iucn.org/wgwap/?7015/Western-gray-whale-makes-unexpected-journey. Accessed 2010 Jun 8.
71. Johnston C, Deméré TA, Berta A, Yonas J, St Leger J, (2010) Observations on the musculoskeletal anatomy of the head of a neonate gray whale (Eschrichtius robustus). Mar Mamm Sci 26: 186-194.
72. Russell D, (2001) Eye of the whale: epic passage from Baja to Siberia New York Simon and Schuster.
73. Dunham JS, Duffus DA, (2002) Diet of gray whales (Eschrichtius robustus) in Clayoquot Sound, British Columbia, Canada. Mar Mamm Sci 18: 419-427.
74. Stelle LL, Megill WM, Kinzel MR, (2008) Activity budget and diving behavior of gray whales (Eschrichtius robustus) in feeding grounds off coastal British Columbia. Mar Mamm Sci 24: 462-478.
75. Pike GC, (1962) Migration and feeding of the gray whale (Eschrichtius gibbosus). J Fish Res Board Canada 19: 815-838.
76. Darling JD, (1984) Gray whales off Vancouver Island, British Columbia. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 267-287.
77. Michel C, Hicks BJ, Stölting KN, Clarke AC, Stevens MI, et al. (2008) Distinct migratory and non-migratory ecotypes of an endemic New Zealand eleotrid (Gobiomorphus cotidianus) - implications for incipient speciation in island freshwater fish species. BMC Evolutionary Biology 8: 49.
78. Rettie WJ, Messier F, (2000) Hierarchical habitat selection by woodland caribou: its relationship to limiting factors. Ecography 23: 466-478.
79. Bolger DT, Newmark WD, Morrison TA, Doak DF, (2008) The need for integrative approaches to understand and conserve migratory ungulates. Ecol Lett 11: 63-77.
80. Addicott WO, (1966) Late Pleistocene marine paleoecology and zoogeography in central California. U.S. Geological Survey Professional Paper 523C: C1-C21.
81. Moore TC, Hutson WH, Kipp N, Hays JD, Prell W, et al. (1981) The biological record of the ice-age ocean. Palaeogeography Palaeoclimatology Palaeoecology 35: 357-370.
82. Gardner SC, Chávez-Rosales S, (2000) Changes in the relative abundance and distribution of gray whales (Eschrichtius robustus) in Magdalena Bay, Mexico during an El Nino Event. Mar Mamm Sci 16: 728-738.
83. Shelden KEW, Rugh DJ, Schulman-Janiger A, (2004) Gray whales born north of Mexico: Indicator of recovery or consequence of regime shift? Ecol Applications 14: 1789-1805.
84. Goebel T, Waters MR, O'Rourke DH, (2008) The Late Pleistocene dispersal of modern humans in the Americas. Science 319: 1497-1502.
85. Erlandson JM, Rick TC, (2010) Archaeology meets marine ecology: the antiquity of maritime cultures and human impacts on marine fisheries and ecosystems. Ann Rev Mar Sci 2: 231-251.
86. Erlandson JM, Rick TC, Vellanoweth RL, Kennett DJ, (1999) Maritime subsistence at a 9300 year old shell midden on Santa Rosa Island, California. J Field Archaeol 26: 255-261.
87. Erlandson JM, Rick TC, (2008) Archaeology, marine ecology, and human impacts on marine environments. In: Rick TC, Erlandson JM, editors. Human Impacts on Ancient Marine Ecosystems: A Global Perspective Berkeley University of California Press pp. 1-19.
88. Burton RK, Snodgrass JJ, Gifford-Gonzalez D, Guilderson T, et al. (2001) Holocene changes in the ecology of northern fur seals: insights from stable isotopes and archaeofauna. Oecologia 128: 107-115.
89. Simenstad CA, Estes JA, Kenyon DW, (1978) Aleuts, sea otters and alternate stable-state communities. Science 200: 403-411.
90. Stewart BC, LeBouef BJ, Yochem PK, Huber HR, Delong RL, et al. (1994) History and present status of the northern elephant seal population. In: LeBouef BJ, Laws RM, editors. Elephant seals, population ecology, behavior, and physiology Berkeley University of California Press pp. 29-48.
91. Mitchell E, (1979) Comments on the magnitude of the early catch of east Pacific gray whale (Eschrichtius robustus). Reports of the International Whaling Commission 29: 307-314.
92. O'Leary BL, (1984) Aboriginal whaling from the Aleutian Islands to Washington State. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 79-102.
93. Krupnick I, (1984) Gray whales and the aborigines of the Pacific Northwest: the history of aboriginal whaling. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 103-120.
94. Mitchell ED, Reeves RR, (1990) Aboriginal whaling for gray whales of the East Pacific stock. Scientific Committee on the Assessment of Gray Whales, Seattle, WA, USA.
95. Moore SE, Huntington HP, (2008) Arctic marine mammals and climate change: impacts and resilience. Ecol App 18 (Supplement): S157-S165.
96. Swartz SL, Taylor BL, Rugh DJ, (2006) Gray whale Eschrichtius robustus population and stock identity. Mamm Rev 36: 66-84.
97. Pauly D, (1995) Anecdotes and the shifting baseline syndrome of fisheries. Trends in Ecol and Evol 10: 430.
98. Dayton PK, Tegner MJ, Edwards PB, Riser KL, (1998) Sliding baselines, ghosts, and reduced expectations in kelp forest communities. Ecol App 8: 309-322.
99. Jackson JBC, Kirby MX, Berger WH, Bjorndal KA, Botsford LW, et al. (2001) Historical overfishing and the recent collapse of coastal ecosystems. Science 293: 629-638.
100. Liljeborg W, (1867) On two subfossil whales discovered in Sweden. Nova Acta Roy Soc Sci Uppsala, Series III, Volume VI pp. 48.
101. Barnes LG, McLeod SA, (1984) The fossil record and phyletic relationships of gray whales. In: Jones ML, Swartz SL, Leatherwood S, editors. The Gray Whale Eschrichtius robustus San Diego Academic Press pp. 3-32.
102. Jacobs SE, (2005) The Pleistocene paleontology and stratigraphy of Palos Verdes Peninsula. In: Brown AR, Shlemon RJ, Cooper JD, editors. pp. 101-120 Geology and paleontology of Palos Verdes Hills, California: A 60th anniversary revisit to commemorate the 1946 publication of U.S.G.S. Professional Survey Paper 207, Pacific Section SEPM 103.
103. Ichishima H, Sato E, Sagayama T, Kimura M, (2006) The oldest record of Eschrichtiidae (Cetacea: Mysticeti) from the Late Pliocene, Hokkaido, Japan. J Paleontology 80: 367-379.
104. Deméré TA, Berta A, McGowen MR, (2005) The taxonomic and evolutionary history of fossil and modern balaenopteroid mysticetes. J Mamm Evol 12: 99-143.
105. Whitmore FC, Kaltenbach JA, (2008) Neogene Cetacea of the Lee Creek Phosphate Mine, North Carolina. Virginia Mus Nat Hist Special Publication 14: 181-269.
106. Bisconti M, Varola A, (2006) The oldest eschrichtiid mystiete and a new morphological diagnosis of Eschrichtiidae (Gray Whales). Rivista Italiana di Paleontologia e Stratigrafia 112: 447-457.
107. Bisconti M, (2008) Morphology and phylogenetic relationships of a new eschrichtiid genus (Cetacea: Mysticeti) from the Early Pliocene of northern Italy. Zool J Linn Soc 153: 161-186.
108. Haq BU, Hardenbol J, Vail PR, (1987) Chronology of fluctuating sea level since the Triassic. Science 235: 1156-1167.
109. Müller RD, Sdrolias M, Gaina C, Steinberger B, Heine C, (2008) Long-term sea-level fluctuations driven by ocean basin dynamics. Science 319: 1357-1362.
110. Thomas AL, Henderson GM, Deschamps P, Yokoyama Y, Mason AJ, et al. (2009) Penultimate deglacial sea-level timing from Uranium/Thorium dating of Tahitian corals. Science 324: 1186-1189.
111. Rohling EJ, Grant K, Bolshaw M, Roberts AP, Siddall M, et al. (2009) Antarctic temperature and global sea level closely coupled over the past five glacial cycles. Nature Geoscience 2: 500-504.
112. Cheng H, Edwards RL, Broecker WS, Denton GH, Kong X, et al. (2009) Ice Age terminations. Science 326: 248-252.
113. Denton GH, Anderson RF, Toggweiler JR, Edwards RL, Schaefer JM, et al. (2010) The last glacial termination. Science 328: 1652-1656.
114. Amante C, Eakins BW, (2009) ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24.
115. Eakins BW, Sharman GF, (2010) Volumes of the World's Oceans from ETOPO1, NOAA National Geophysical Data Center website. Available: http://www.ngdc.noaa.gov/mgg/global/etopo1_ocean_volumes.html. Accessed 2010 June 8.