Climate change clues from tiny marine algae – ancient and modern

Microscopic ocean algae called coccolithophores are providing clues about the impact of climate change both now and many millions of years ago. The study found that their response to environmental change varies between species, in terms of how quickly they grow.

Coccolithophores, a type of plankton, are not only widespread in the modern ocean but they are also prolific in the fossil record because their tiny calcium carbonate shells are preserved on the seafloor after death – the vast chalk cliffs of Dover, for example, are almost entirely made of fossilised coccolithophores.

Species-specific growth response of coccolithophores to Palaeocene–Eocene environmental change

Coccolithophores—single-celled calcifying phytoplankton—represent an essential footing to marine ecosystems, yet their sensitivity to environmental change, and in particular increases in atmospheric CO₂, is poorly understood¹. During the Palaeocene–Eocene Thermal Maximum (PETM), about 56 million years ago, atmospheric CO₂ concentrations rose rapidly and the oceans acidified^{2, 3}, making this an ideal time interval to examine coccolithophore responses to environmental change. Here we compare the results of experiments on modern coccolithophore species with exceptional fossil coccosphere records of the PETM, providing a cellular-level perspective. In modern taxa, we find that during the exponential growth phase of rapid cell division, small cells with few coccoliths are produced, whereas larger cells with more coccoliths are produced during slowed cell division. Applying these diagnostic features to the PETM fossil record, we find that the dominant species exhibited different growth responses to the environmental forcing. Toweius pertusus shows geometry indicative of rapid cell division. In contrast, we suggest that cells of Coccolithus pelagicus grew more slowly during the period of environmental change. In the modern ocean, Emiliania huxleyi, which is closely related to the extinct T. pertusus, is prolific and widespread, whereas C. pelagicus is more limited in range and abundance. We argue that these different responses to environmental change were critical to the post-PETM evolutionary success of the descendants of these taxa.

An automated system for spectrophotometric seawater pH measurements

Spectrophotometric pH measurements stand to benefit greatly from the consistency and speed made possible through automation. Here we describe a simple, fast, and precise automated spectrophotometric pH measurement system for seawater samples. The system requires 4 min per analysis, consumes 60 mL seawater from a sample bottle, and requires little operator interaction to obtain repeatability comparable with the best results published with other techniques (± 0.0004). The system and the suggested sample handling methods are assessed using over 5000 at-sea measurements obtained during a hydrographic cruise in the Indian Ocean. We estimate the overall measurement uncertainty of the existing, pre-2011, body of at-sea spectrophotometric pH measurements—made using these methods or otherwise—to currently be in the range of 0.01 to 0.02 pH units. However, a new approach for using purified dyes at a range of temperatures and salinities (Liu et al. 2011) stands to greatly reduce this uncertainty for future spectrophotometric pH measurements: our assessment suggests that the overall uncertainty should improve to ~0.005 pH units if dye impurities and the indicator’s temperature and salinity sensitivity are adequately addressed. Any such improvement in measurement accuracy may provide a basis from which to determine adjustments appropriate for the existing body of spectrophotometric pH measurements made using commercially available (and impure) dyes.

A trace-metal clean, pH-controlled incubator system for ocean acidification incubation studies

The emerging research field of ocean acidification studies has gained international attention during the past years and recently defined international standards in the Guide to best practices for ocean acidification research and data reporting. However, a combination of ocean acidification studies with trace metal research is very rare and possible trace metal side effects on marine phytoplankton in ocean acidification incubation studies are often not assessed. Here we describe a trace metal clean, pH-controlled incubator system for laboratory and seagoing ocean acidification research. Seawater pH adjustment is achieved via passing CO₂ gas through diffusive silicone tubing to minimize the risk of contamination and to avoid the negative mechanical effects of gas bubbles on phytoplankton. The system measures pH automatically with an accuracy of 0.004 and a precision of 0.001 and includes a feedback regulation to adjust pH during the incubation if required. Mn, Fe, Co, Ni, Cd, and Pb measurements show that our system and the pH adjustment method do not contaminate the samples with any of these metals. We tested this system in laboratory studies as well as during the PINTS voyage in the Tasman Sea.

Anthropogenic changes to seawater buffer capacity combined with natural reef metabolism induce extreme future coral reef CO2 conditions

Ocean acidification, via an anthropogenic increase in seawater carbon dioxide (CO₂), is potentially a major threat to coral reefs and other marine ecosystems. However, our understanding of how natural short-term diurnal CO₂ variability in coral reefs influences longer-term anthropogenic ocean acidification is unclear. Here we combine observed natural carbonate chemistry variability with future carbonate chemistry predictions for a coral reef flat in the Great Barrier Reef based on the RCP8.5 CO₂ emissions scenario. Rather than observing a linear increase in reef flat partial pressure of CO₂ (pCO₂) in concert with rising atmospheric concentrations, the inclusion of in situ diurnal variability results in a highly non-linear 3-fold amplification of the pCO₂ signal by the end of the century. This significant non-linear amplification of diurnal pCO₂ variability occurs as a result of combining natural diurnal biological CO₂ metabolism with long-term decreases in seawater buffer capacity, which occurs via increasing anthropogenic CO₂ absorption by the ocean. Under the same benthic community composition, the amplification in the variability of pCO₂ is likely to lead to exposure to mean maximum daily pCO₂ levels of ~2100 μatm, with corrosive conditions with respect to aragonite by end-century at our study site. Minimum pCO₂ levels will become lower relative to the mean offshore value (~3-fold increase in the difference between offshore and minimum reef flat pCO₂) by end-century, leading to a further increase in the pCO₂ range that organisms are exposed to. The biological consequences of short-term exposure to these extreme CO₂ conditions, coupled with elevated long-term mean CO₂ conditions are currently unknown and future laboratory experiments will need to incorporate natural variability to test this. The amplification of pCO₂ that we describe here is not unique to our study location, but will occur in all shallow coastal environments where high biological productivity drives large natural variability in carbonate chemistry.

ENVIRONMENT: Speaker looks at ocean acidification’s impact on fish

Scott Steltzner, a fisheries biologist with the Squaxin Island Tribe, will be the next presenter in the Discovery Speakers Series.

Steltzner will give his presentation Thursday, the final program in the 2012-13 series.

Working for the tribe the past nine years, Steltzner’s research has included early marine survival of salmonids and assessment of nearshore habitats. He has done a lot of study on the survival of coho after they are released from the tribe’s net pens. He holds a degree in marine biology from San Diego State University.

Ocean acidification (video)

Ocean acidification from NIWA on Vimeo.

Otago water shows how the ocean is changing.

For the last 14 years, in collaboration with the University of Otago’s Chemistry Department, Dr Kim Currie has run a time series tracking ocean acidification. Every two months, she collects water samples along a 65-kilometre line from the tip of Otago Harbour out into subantarctic waters.

Changes in ocean put shellfish business in jeopardy

EVERETT — Between 2005 and 2009, billions of oyster larvae began dying at hatcheries around the state before anyone knew what was going on or could do anything about it.

The state’s $270 million shellfish industry, which employs about 3,200 people, is in danger.

One oyster farm, Goose Point Oysters in Willapa Bay, has begun raising oyster larvae in Hawaii because it can no longer grow them here.

The reason, scientists say, is ocean acidification.

“The problem’s not going away,” said Ian Jefferds, general manager and co-owner of Penn Cove Shellfish in Coupeville.

Benthic buffers and boosters of ocean acidification on coral reefs

Ocean acidification is a threat to marine ecosystems globally. In shallow-water systems, however, ocean acidification can be masked by benthic carbon fluxes, depending on community composition, seawater residence time, and the magnitude and balance of net community production (p_n) and calcification (g_n). Here, we examine how six benthic groups from a coral reef environment on Heron Reef (Great Barrier Reef, Australia) contribute to changes in seawater aragonite saturation state (Ω_a). Results of flume studies showed a hierarchy of responses across groups, depending on CO₂ level, time of day and water flow. At low CO₂ (350–450 μatm), macroalgae (Chnoospora implexa), turfs and sand elevated Ω_a of the flume water by around 0.10 to 1.20 h⁻¹ – normalised to contributions from 1 m² of benthos to a 1 m deep water column. The rate of Ω_aincrease in these groups was doubled under acidification (560–700 μatm) and high flow (35 compared to 8 cm s⁻¹). In contrast, branching corals (Acropora aspera) increased Ω_a by 0.25 h⁻¹ at ambient CO₂(350–450 μatm) during the day, but reduced Ω_a under acidification and high flow. Nighttime changes in Ω_a by corals were highly negative (0.6–0.8 h⁻¹) and exacerbated by acidification. Calcifying macroalgae (Halimeda spp.) raised Ω_a by day (by around 0.13 h⁻¹), but lowered Ω_a by a similar or higher amount at night. Analyses of carbon flux contributions from four different benthic compositions to the reef water carbon chemistry across Heron Reef flat and lagoon indicated that the net lowering of Ω_a by coral-dominated areas can to some extent be countered by long water residence times in neighbouring areas dominated by turfs, macroalgae and potentially sand.

Arctic microbial community dynamics influenced by elevated CO2 levels (update)

The Arctic Ocean ecosystem is particularly vulnerable to ocean acidification (OA) related alterations due to the relatively high CO₂ solubility and low carbonate saturation states of its cold surface waters. Thus far, however, there is only little known about the consequences of OA on the base of the food web. In a mesocosm CO₂-enrichment experiment (overall CO₂ levels ranged from ~ 180 to 1100 μatm) in Kongsfjorden off Svalbard, we studied the consequences of OA on a natural pelagic microbial community. OA distinctly affected the composition and growth of the Arctic phytoplankton community, i.e. the picoeukaryotic photoautotrophs and to a lesser extent the nanophytoplankton thrived. A shift towards the smallest phytoplankton as a result of OA will have direct consequences for the structure and functioning of the pelagic food web and thus for the biogeochemical cycles. Besides being grazed, the dominant pico-and nanophytoplankton groups were found prone to viral lysis, thereby shunting the carbon accumulation in living organisms into the dissolved pools of organic carbon and subsequently affecting the efficiency of the biological pump in these Arctic waters.