Category Archives: Oceans

Great Barrier Reef corals can withstand pH variations

McCulloch M.T. et al. (2018) Boron Isotopic Systematics in Scleractinian Corals and the Role of pH Up-regulation. In: Marschall H., Foster G. (eds) Boron Isotopes. Advances in Isotope Geochemistry. Springer, Cham  https://doi.org/10.1007/978-3-319-64666-4_6

The boron isotopic composition (δ11B) of scleractinian corals has been used to track changes in seawater pH and more recently as a probe into the processes controlling bio-calcification. For corals that precipitate aragonite skeletons, up-regulation of pH appears to be a general characteristic, typically being ~0.3 to ~0.6 pH units higher than ambient seawater. The relationship between the pH of the corals calcifying-fluid (pHcf) and seawater pHT (total scale) is shown to be dependent on both physiological as well environmental factors. In laboratory experiments conducted on symbiont-bearing (zooxanthellate) corals under conditions of constant temperature and seawater pH, changes in the δ11B derived calcifying fluid pHcf is typically 1/3 to 1/2 of that of ambient seawater. Similar linear relationships are found for cold water corals that live in relatively stable, cold, deep-water environments but at significantly elevated levels of pHcf(~0.5–1 pH units above seawater), a likely response to the lower pH of their deep-sea environments. In contrast, zooxanthellae-bearing corals living in shallow-water reef environments that experience significant natural variations in temperature, light, nutrients and seawater pH, show different types of responses. For example, over seasonal time-scales Poritescorals from the Great Barrier Reef (GBR) have a large range in pHcf of ~8.3 to ~8.5, significantly greater (~×2 to ~×3) than that of reef-water (pHT ~8.01 to ~8.08), and an order of magnitude greater than that expected from ‘static’ laboratory experiments. Strong physiological controls, but of a different character, are found in corals grown in a Free Ocean Carbon Enrichment Experiment (FOCE) conducted in situ within the Heron Island lagoon (GBR). These corals exhibit near constant pHcf values regardless of external changes in temperature and seawater pH. This pattern of strong physiologically controlled ‘pHhomeostasis’, with elevated but constant pHcf has been found despite large natural seasonal variations in the pH (±0.15 pH units) of the lagoon waters, as well as the even larger super-imposed decreases in seawater pH (~0.25 pH units) designed to simulate year 2100 conditions. In natural reef environments we thus find that the processes influencing the up-regulation of pHcf in symbiont-bearing corals are subject to strong physiological controls, behaviour that is not well simulated in the current generation of aquaria-based experiments with fixed seawater pH and temperature. Conversely, cold-water corals that lack symbionts and inhabit the relatively stable deep-sea environments hold the best prospects for providing reliable reconstructions of seawater pH. Clearly, further studies utilising the δ11B-pHcfproxy combined with other DIC/carbonate-ion proxies (e.g. B/Ca), but conducted under realistic ‘natural’ conditions, are required to elucidate the processes controlling coral bio-calcification and to better understand the vulnerability of scleractinian corals to anthropogenic driven warming and ocean acidification.

No direct effects of ocean acidification observed in Arctic specie

Peter Thor, Fanny Vermandele, Marie-Helene Carignan, Sarah Jacque, Piero Calosi.  No maternal or direct effects of ocean acidification on egg hatching in the Arctic copepod Calanus glacialis PLOS ONE 13(2): e0192496. https://doi.org/10.1371/journal.pone.0192496

Widespread ocean acidification (OA) is transforming the chemistry of the global ocean and the Arctic is recognised as the region where this transformation will occur at the fastest rate. Moreover, many Arctic species are considered less capable of tolerating OA due to their lower capacity for acid-base regulation. This inability may put severe restraints on many fundamental functions, such as growth and reproductive investments, which ultimately may result in reduced fitness. However, maternal effects may alleviate severe effects on the offspring rendering them more tolerant to OA. In a highly replicated experiment we studied maternal and direct effects of OA predicted for the Arctic shelf seas on egg hatching time and success in the keystone copepod species Calanus glacialis. We incubated females at present day conditions (pHT 8.0) and year 2100 extreme conditions (pHT 7.5) during oogenesis and subsequently reciprocally transplanted laid eggs between these two conditions. Statistical tests showed no effects of maternal or direct exposure to OA at this level. We hypothesise that Cglacialis may be physiologically adapted to egg production at low pH since oogenesis can also take place at conditions of potentially low haemolymph pH of the mother during hibernation in the deep.

Evidence lacking for ocean acidification by carbon dioxide

Paul McElhany. CO2 sensitivity experiments are not sufficient to show an effect of ocean acidification. ICES Journal of Marine Science, Volume 74, Issue 4, 1 May 2017, Pages 926–928,https://doi.org/10.1093/icesjms/fsw085

“The ocean acidification (OA) literature is replete with laboratory studies that report species sensitivity to seawater carbonate chemistry in experimental treatments as an “effect of OA”. I argue that this is unintentionally misleading, since these studies do not actually demonstrate an effect of OA but rather show sensitivity to CO2. Documenting an effect of OA involves showing a change in a species (e.g. population abundance or distribution) as a consequence of anthropogenic changes in marine carbonate chemistry. To date, there have been no unambiguous demonstrations of a population level effect of anthropogenic OA, as that term is defined by the IPCC.”

State-of-the-art computer models fail to reproduce recent ocean cooling

Jing-Jia Luo, Gang Wang, Dietmar Dommenget. Many common model biases reduce CMIP5’s ability to simulate the recent Pacific La Niña-like cooling? Climate Dynamics, February 2018, Volume 50, Issue 3–4, pp 1335–1351

Over the recent three decades sea surface temperate (SST) in the eastern equatorial Pacific has decreased, which helps reduce the rate of global warming. However, most CMIP5 model simulations with historical radiative forcing do not reproduce this Pacific La Niña-like cooling. Based on the assumption of “perfect” models, previous studies have suggested that errors in simulated internal climate variations and/or external radiative forcing may cause the discrepancy between the multi-model simulations and the observation. But the exact causes remain unclear. Recent studies have suggested that observed SST warming in the other two ocean basins in past decades and the thermostat mechanism in the Pacific in response to increased radiative forcing may also play an important role in driving this La Niña-like cooling. Here, we investigate an alternative hypothesis that common biases of current state-of-the-art climate models may deteriorate the models’ ability and can also contribute to this multi-model simulations-observation discrepancy. Our results suggest that underestimated inter-basin warming contrast across the three tropical oceans, overestimated surface net heat flux and underestimated local SST-cloud negative feedback in the equatorial Pacific may favor an El Niño-like warming bias in the models. Effects of the three common model biases do not cancel one another and jointly explain ~50% of the total variance of the discrepancies between the observation and individual models’ ensemble mean simulations of the Pacific SST trend. Further efforts on reducing common model biases could help improve simulations of the externally forced climate trends and the multi-decadal climate fluctuations.

Ocean temperature study assumptions requires great faith

Bernhard Bereiter, Sarah Shackleton, Daniel Baggenstos, Kenji Kawamura, Jeff Severinghaus. Mean global ocean temperatures during the last glacial transition Nature 553, 39–44 (04 January 2018) doi: 10.1038/nature25152

Little is known about the ocean temperature’s long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

Ocean Cycles Likely Behind Recent Climate Changes

“An eminent atmospheric scientist says that natural cycles may be largely responsible for climate changes seen in recent decades. In a new report published by the Global Warming Policy Foundation, Anastasios Tsonis, emeritus distinguished professor of atmospheric sciences at the University of Wisconsin-Milwaukee, describes new and cutting-edge research into natural climatic cycles, including the well known El Nino cycle and the less familiar North Atlantic Oscillation and Pacific Decadal Oscillation.” click here

Natural Ocean Acidification Good for Fish

“The real story here is that past scares claiming that ocean acidification would create reckless fish were most likely an artefact of an inadequate experiment. There are big swings of CO2 and pH in shallow water environments, and the normal day-night cycle turns out to be good for fish. Putting them in a laboratory tank without these daily changes may create fish that behave badly. So ocean acidification is not only natural, but a good and necessary thing.” click here