Ocean Circulation Modes of the Phanerozoic: Implications for the Antiquity of Deep-Sea Benthonic Invertebrates

Abstract

It has been suggested that some modern anchialine cave invertebrates originated from deepsea ancestors of considerable antiquity (>100 million years). An alternative view is that such taxa could not have a long bathyal/abyssal history because of extended periods of anoxia in the oceans during the Mesozoic and Cainozoic, and that consequently their ancestors should be sought among shallow-water fauna. In order to assist in the evaluation of these opposing hypotheses, the Phanerozoic record of oxygen-deficient conditions in the water column is reviewed, with special regard for postulated ''anoxic events'' as a causative mechanism for major changes in biodiversity (e.g., mass extinctions). A key issue is the relative importance, through the Phanerozoic, of two types of deep ocean circulation: Halothermal Circulation (HTC), involving the formation of Warm Saline Deep Water (WSDW) in the tropics, promotes anoxia, while Thermohaline Circulation (THC), characterized by Cold Deep Water (CDW) formed at high latitudes, ventilates the deep ocean. Particular attention is paid to the evidence of the mid-Cretaceous Cenomanian-Turonian Boundary Event. The (apparently) widely accepted view that the deep ocean was mainly anoxic until about 40 million years ago (the time of origin of the modern psychrosphere) is challenged. Evidence from the deep-ocean record of bioturbated sediments suggests that there has been a Cold Deep Water component in ocean circulation for at least the last 90 million years (mid-Cretaceous onwards) and possibly throughout the Phanerozoic. This conclusion has important implications for hypotheses about the antiquity of deep-ocean benthonic invertebrate faunas. Es wurde vorgeschlagen, dass moderne, anchialine Hohleninvertebraten von Tiefseeformen bedeutenden Alters (>100 Millionen Jahre) abstammen. Eine alternative Ansicht besagt, dass solche Taxa aufgrund ausgedehnter, anoxischer Perioden im Mesozoikum und Kanozoikum keine besonders lange bathyale/abyssale Geschichte haben k onnen. Ihre Vorfahren solten daher bei Flachwasserformen gesucht werden. Um zur Evaluierung dieser gegensatzlichen Hypothesen beizutragen, werden Indizien fur sauerstoffarme Verhaltnisse in der Wassersaule wahrend des Phanerozoikums einer neuen Begutachtung unterzogen, mit bezonderer Berucksichtigung postulierter ''anoxischer Ereignisse'' als kausalem Mechanismus fur grossere Anderungen in der Biodiversitat (z. B. Massen-Aussterben). Ein Schlusselfaktor ist die relative Bedeutung zweier Typen von Tiefsee-Zirkulationen wahrend des Phanerozoikums. Die halothermale Zirkulation (Halothermal Curculation, HTC), die zur Bildung warmen, salinen Tiefenwassers (Warm Saline Deep Water, WSDW) in den Tropen fuhrt, fordert Anoxie, wahrend die thermohaline Zirkulation (Thermohaline Circulation, THC), charakterisiert durch in hohen Breiten gebildetes, kaltes Tiefenwasser (Cold Deep Water, CDW) die Tiefsee ventiliert. Besonderes Augenmerk wird auf die Ereignisse an der Cenoman-Turon-Grenze (Mittlere Kreide) gelegt. Die (offensichtlich) weithin akzeptierte Ansicht, dass die Tiefsee bis vor 40 Millionen Jahren grossteils anoxisch war (der Ursprungszeitpunkt der modernen Psychrosphare), wird in Frage gestellt. Hinweise auf durch Bioturbation gestorte TiefseeSedimente lassen vermuten, dass eine kalte Tiefenwasser-Komponente bei den Meereszirkulationen seit mindestens 90 Millionen Jahren (seit der mittleren Kreide), und moglicherweise wahrend des gesamten Phanerozoikums, existiert hat. Diese Schlussfolgerung hat wichtige Auswirkungen auf Hypothesen uber das Alter der benthischen Tiefsee-Evertebratenfauna.

Temporary expansion to shelf depths rather than an onshore-offshore trend: the shallow-water rise and demise of the modern deep-sea brittle star family Ophiacanthidae (Echinodermata: Ophiuroidea)

“…During much of the mid-and Late Mesozoic, the prevailing mechanism of deep-water formation was halothermal circulation, the sinking of warm, high-salinity surface waters at low latitudes (Horne 1999). As a consequence, deep water masses were relatively warm (>10°C) during most of the later Mesozoic (e.g.…”

The dynamics of biogeographic ranges in the deep sea

“…34 Ma). Deep-ocean circulation has alternated between two historical ocean types one driven by high-latitude deepwater formation (thermohaline, THC), resulting in cold, oxygenated deep water, and one driven by salinityinduced stratification at low latitudes (halothermal, HTC) resulting in warm, saline deep water and reduced global circulation (Jeppsson 1990;Horne 1999;Rogers 2000). THC conditions have prevailed since the Eocene/Oligocene transition, but a warmer, low-oxygen HTC phase dated back to the Triassic.…”

“…THC conditions have prevailed since the Eocene/Oligocene transition, but a warmer, low-oxygen HTC phase dated back to the Triassic. During this period, deep-water anoxia was frequent and widespread (Jacobs & Lindberg 1998;Rogers 2000;Waelbroeck et al 2001), with the most severe events associated with rapid THC -HTC transitions in the mid-Cretaceous, and at the Permian/Triassic and Ordovician/Silurian boundaries (Horne 1999).…”

“…Most current hypotheses for the origins of the deepsea fauna centre on 'extinction and replacement'-a near-complete extinction of deep-sea fauna triggered by catastrophic anoxic events, with subsequent invasion and radiation of shallow-water species into the deep (Rogers (2000), reviewed in Horne 1999;Wilson 1999). Thus, the deep-sea fauna may be relatively young, dating back to the last major anoxic event at the Eocene/Oligocene boundary (reviewed in Wilson (1999)).…”

Pressure tolerance of the shallow-water caridean shrimp Palaemonetes varians across its thermal tolerance window

“…Though the origin and antiquity of extant deep-sea fauna is uncertain, it is generally considered that climate-driven extinction events in the deep sea, and subsequent re-colonisation of this realm, took place during many geological ages (Jablonski et al, 1983;Horne, 1999;Wilson, 1999;Aquino-Souza et al, 2008). As such, extant deep-sea fauna are considered to comprise both ancient and more recent shallowwater lineages (Horne, 1999;Wilson, 1999).…”