Das Gedächtnis der Meere : Korallenriffe speichern Klimadaten

Tropische Korallenriffe sind die artenreichsten Ökosysteme im Ozean. Die »tropischen Regenwälder der Meere« beherbergen zirka 800 Korallenarten und mehrere zehntausend Arten aus fast allen bekannten Tierstämmen. Korallenriffe bedecken weltweit eine Fläche von 600.000 Quadratkilometern, das sind 0,17 Prozent der Erdoberfläche. Sie treten als nahe der Küste gelegene Saumriffe, küstenfernere Barriereriffe, ringförmige Atolle und flache Karbonat-Plattformen auf . Der Begriff »Karbonat« weist darauf hin, dass Korallen als Riffbildner ein Skelett aus Kalk haben. Auch Kalkalgen und Weichtiere wie Muscheln und Schnecken sind durch die Bildung von Kalkskeletten und Kalkschalen am Riffaufbau beteiligt. Da tropische Korallenriffe nur in der Nähe der Meeresoberfläche wachsen, können Geowissenschaftler mit Hilfe fossiler Korallenfunde ermitteln, wie sich der Pegel des Meeresspiegels in vergangenen Jahrtausenden entwickelt hat. Auch andere wichtige Klimadaten wie Wassertemperatur, Sonneneinstrahlung und Kohlendioxid-Gehalt der Atmosphäre sind in Korallenriffen »gespeichert«. Frankfurter Geowissenschaftler erschließen diese wichtigen Daten, die weit vor menschliche Messungen zurückreichen, durch systematische Bohrungen in Korallenriffen der Karibik, des Persischen Golfs und der Malediven

Braquiópodos recientes del golfo Pérsico y su significación geográfica

Two brachiopod species Discradisca indica (Dall, 1920) and Argyrotheca jacksoni Cooper, 1973, together with Lingula sp., have been identified from the Persian Gulf. These species, added to the two species Terebratulina retusa (Linnaeus, 1758) and Megerlia truncata (Linnaeus, 1767) previously identified by Jackson (1921), and Lingula anatina Lamarck, 1819 by Emig (1988) bring the total to 5 species for the region. The genera Discradisca and Argyrotheca are recorded for the first time from the Persian Gulf. This fauna shows biogeographical affinities to the Indian Ocean and the Mediterranean faunas. The disjunct geographical distribution of Discradisca suggests this genus is a relict of an ancient Tethyan fauna.Se identificaron dos especies de braquiópodos, Discradisca indica (Dall, 1920) y Argyrotheca jacksoni Cooper, 1973, junto con Lingula sp., en material procedente del Golfo Pérsico. Estas especies, junto con las previamente identificadas por Jackson en 1921, Terebratulina retusa (Linnaeus, 1758) y Megerlia truncata (Linnaeus, 1767), y por Emig (1988), Lingula anatina Lamarck, 1819, elevan a cinco el total de especies reconocidas en la región. Los géneros Discradisca y Argyrotheca se dan a conocer por vez primera en el Golfo Pérsico. Las especies estudiadas muestran una relación biogeográfica con las presentes en el océano Índico y en el mar Mediterráneo. La distribución geográfica disjunta observada del género Discradisca, sugiere que se trata de un género que, presente en el antiguo Tetis, ha logrado sobrevivir sólo en determinados refugios mientras que se ha extinguido en los demás

Late glacial to deglacial variation of coralgal assemblages in the Great Barrier Reef, Australia

Integrated Ocean Drilling Program (IODP) Expedition 325 cored submerged reefs along the shelf edge of the Great Barrier Reef (GBR) to study sea-level and environmental changes and their impacts on reef communities and reef growth since the Last Glacial Maximum (LGM). Previous work defined five reef sequences (Reef 1–5) that span the last 30,000 years. Here we examined the variation in coralgal assemblages and their paleoenvironmental settings in late glacial to deglacial sequences from 23 holes cored seaward of the modern GBR in water depths from 46 to 131 m along four transects at three localities: Hydrographers Passage (HYD-01C and HYD-02A), Noggin Pass (NOG–01B), and Ribbon Reef (RIB-02A). We identified three coralline algal assemblages and eight coral assemblages indicating a broad range of reef settings from the shallow reef crest (0–5 m) to the deep forereef slope (>20 m). We document in detail for the first time the distribution and composition of reef communities that grew in the GBR during the LGM from 22,000–19,000 years ago. They included coral taxa that are major reef builders today: Isopora, Acropora gr. humilis, Dipsastraea gr. pallida, Porites, and Montipora. Prior to the fall in sea level to the maximum extent of the LGM, late glacial reef communities developed more proximally (landward) to the modern GBR along the shelf edge. Their distribution and composition reflect influences of the older Pleistocene basement depth and possible terrigenous sediment inputs. Post-LGM deglacial reef growth was vigorous in proximal sites and characterized by the accretion of a very shallow high-energy coralgal assemblage composed of medium to robustly branching Acropora, including A. gr. humilis, and thick algal crusts of Porolithon gr. onkodes associated with vermetid gastropods. More distally, reef growth was variably impacted by terrigenous input following deglacial reflooding of antecedent reef terraces. The coralgal succession and sedimentary facies in Noggin Pass indicate that an early drowning trend was linked to increased turbidity that was likely controlled by shelf morphology (narrow shelf, steep slope) and/or proximity to a paleo-river mouth. The deglacial succession in Ribbon Reef lacks typical shallow-water indicators, which may reflect influences of the particularly steep slope of the northern GBR shelf edge on reef zonation. A major sea-level jump at the onset of the Younger Dryas displaced reef habitats further upslope, forming a barrier reef system mainly composed of robustly branching acroporids distinct from the more distal sites. Our results highlight the importance of sedimentation and shelf morphology in addition to relative sea-level changes in controlling variations in reef community over centennial to millennial timescales. © 2019 Elsevier B.V.Australian Research Council-DP109400