Der pH-Wert der Ozeane hat sich in den letzten Jahrzehnten leicht von 8,15 auf 8,05 reduziert. Obwohl diese Werte noch immer deutlich im alkalischen Bereich liegen (der bis pH 7 reicht), wird in der Fachsprache von einer „Ozeanversauerung“ gesprochen. Der Trend ist deutlich und wird von allen Akteuren der Klimadiskussion anerkannt. Mithilfe von Satelliten kann der pH-Wert der Ozeane heute bequem ermittelt werden.
Die Debatte dreht sich vor allem um die Folgen, die diese leichte pH-Veränderung bei den Meeresbewohnern auslösen könnte. Lange glaubte man, dass sich hier möglicherweise eine Katastrophe anbahnt. Als man sich die Thematik dann im Rahmen von einer Vielzahl von Studien näher anschaute, gab es eine Teilentwarnung. Es ist zum Glück doch nicht so schlimm, wie einige Forscher zunächst befürchtet hatten. Im Folgenden wollen wir die aktuellen Ergebnisse aus der Wissenschaft vorstellen.
Im Februar 2016 erschien im Journal of Marine Science ein Sonderband zur Ozeanversauerung. In einem einleitenden Übersichtsartikel ruft Howard Browman die Forschergemeinde zu verstärktem Skeptizismus auf. Durch die bevorzugte Publikation von dramatisierenden Artikeln sei in der Literatur eine inhaltliche Schieflage entstanden, die es auzugleichen gilt. Hier der Abstract seines Beitrags:
Applying organized scepticism to ocean acidification research
“Ocean acidification” (OA), a change in seawater chemistry driven by increased uptake of atmospheric CO2 by the oceans, has probably been the most-studied single topic in marine science in recent times. The majority of the literature on OA report negative effects of CO2 on organisms and conclude that OA will be detrimental to marine ecosystems. As is true across all of science, studies that report no effect of OA are typically more difficult to publish. Further, the mechanisms underlying the biological and ecological effects of OA have received little attention in most organismal groups, and some of the key mechanisms (e.g. calcification) are still incompletely understood. For these reasons, the ICES Journal of Marine Science solicited contributions to this special issue. In this introduction, I present a brief overview of the history of research on OA, call for a heightened level of organized (academic) scepticism to be applied to the body of work on OA, and briefly present the 44 contributions that appear in this theme issue. OA research has clearly matured, and is continuing to do so. We hope that our readership will find that, when taken together, the articles that appear herein do indeed move us “Towards a broader perspective on ocean acidification research”.
Im Oktober 2015 hatte bereits die James Cook University in einer Pressemitteilung darauf hingewiesen, dass sich das Wachstum einiger Organismengruppen unter saureren Bedingungen sogar verbessert:
Scientists find some thrive in acid seas
Researchers from James Cook University have found that ocean acidification may not be all bad news for one important sea-dwelling plant.
A JCU team led by Dr Catherine Collier studied seagrass growing near underwater volcanic vents in PNG. Carbon dioxide from the vents increases the acidity of nearby water. The researchers found that the more acidic the water was, the more the plant grew. „The increased growth has nothing to do with the acidified water as such, but increased acidification means more carbon, which means the seagrass photosynthesises quicker,“ said Dr Collier. Seagrass provides food and habitat to many species and is a significant carbon sink — soaking up 15 percent of the carbon stored in the ocean every year. But pollution and development mean the plants are declining at a rate of seven per cent a year. Dr Collier said every one of the ten varieties of seagrass so far tested had done better in acidified water. But there were still questions over whether other aspects of climate change would adversely affect them. „On the one hand, if acidification increases seagrass growth, they will be able to absorb more carbon from the ocean, which may slow the acidification. On the other hand, acidification is bad for coral, and erosion of the reef and rising sea levels could have detrimental effects on the seagrass meadows it protects,“ said Dr Collier. She said more investigation, incorporating other variables in the seagrass environment, needed to be done.
NOAA-Wissenschaftler mussten zudem kürzlich einräumen, dass es noch immer keinen Ort auf der Erde gibt, wo eindeutige Schäden aufgrund der Ozeanverauerung zu beklagen wären. Dieses wichtige Eingeständnis machten sie jedoch nicht in einem öffentlichen Bericht, sondern entstammt einer Emailkorrespondenz, die erst auf juristischem Wege ans Licht kam. Auszug aus Quadrant Online:
The [New York Times] editor asked,
„It’s very interesting, but in order to work for us it needs to be geared more toward the general reader. Can the authors give us more specific, descriptive images about how acidification has already affected the oceans? Is the situation akin to the acid rain phenomenon that hit North America? What can be done to counteract the problem?“
Dr Busch, who works for NOAA’s Ocean Acidification Program and Northwest Fisheries Science Center at Seattle, responded to Ms Applebaum:
„Unfortunately, I can’t provide this information to you because it doesn’t exist. As I said in my last email, currently there are NO areas of the world that are severely degraded because of OA or even areas that we know are definitely affected by OA right now. If you want to use this type of language, you could write about the CO2 vent sites in Italy or Polynesia as examples of things to come. Sorry that I can’t be more helpful on this!“
Im Juli 2015 beklagten sich Christopher Cornwall und Catriona Hurd im Fachblatt Ocean Acidification darüber, dass ein großer Teil der Laborexperimente zur Ozeanversauerung methodisch fehlerhaft seien. Daniel Cressey berichtete darüber in Nature:
Crucial ocean-acidification models come up short
Poorly designed studies leave future uncertain for sea dwellers. […] according to a survey published last month by marine scientist Christopher Cornwall, who studies ocean acidification at the University of Western Australia in Crawley, and ecologist Catriona Hurd of the University of Tasmania in Hobart, Australia, most reports of such laboratory experiments either used inappropriate methods or did not report their methods properly.
Lesenswerte Zusammenfassungen zur Ozeanversauerungsforschung erschienen auch kürzlich von Alan Longhurst and Patrick Moore (pdf hier).
