Responses of the metabolism of the larvae of Pocillopora damicornis to ocean acidification and warming

Ocean acidification and warming are expected to threaten the persistence of tropical coral reef ecosystems. As coral reefs face multiple stressors, the distribution and abundance of corals will depend on the successful dispersal and settlement of coral larvae under changing environmental conditions. To explore this scenario, we used metabolic rate, at holobiont and molecular levels, as an index for assessing the physiological plasticity of Pocillopora damicornis larvae from this site to conditions of ocean acidity and warming. Larvae were incubated for 6 hours in seawater containing combinations of CO2 concentration (450 and 950 µatm) and temperature (28 and 30°C). Rates of larval oxygen consumption were higher at elevated temperatures. In contrast, high CO2 levels elicited depressed metabolic rates, especially for larvae released later in the spawning period. Rates of citrate synthase, a rate-limiting enzyme in aerobic metabolism, suggested a biochemical limit for increasing oxidative capacity in coral larvae in a warming, acidifying ocean. Biological responses were also compared between larvae released from adult colonies on the same day (cohorts). The metabolic physiology of Pocillopora damicornis larvae varied significantly by day of release. Additionally, we used environmental data collected on a reef in Moorea, French Polynesia to provide information about what adult corals and larvae may currently experience in the field. An autonomous pH sensor provided a continuous time series of pH on the natal fringing reef. In February/March, 2011, pH values averaged 8.075±0.023. Our results suggest that without adaptation or acclimatization, only a portion of naïve Pocillopora damicornis larvae may have suitable metabolic phenotypes for maintaining function and fitness in an end-of-the century ocean.

Seawater carbonate chemistry and copepod Centropages tenuiremis feeding, filtering and respiration rate during experiments, 2012

Climate change mediates marine chemical and physical environments and therefore influences marine organisms. While increasing atmospheric CO2 level and associated ocean acidification has been predicted to stimulate marine primary productivity and may affect community structure, the processes that impact food chain and biological CO2 pump are less documented. We hypothesized that copepods, as the secondary marine producer, may respond to future changes in seawater carbonate chemistry associated with ocean acidification due to increasing atmospheric CO2 concentration. Here, we show that the copepod, Centropages tenuiremis, was able to perceive the chemical changes in seawater induced under elevated CO2 concentration (>1700 µatm, pH < 7.60) with avoidance strategy. The copepod's respiration increased at the elevated CO2 (1000 µatm), associated acidity (pH 7.83) and its feeding rates also increased correspondingly, except for the initial acclimating period, when it fed less. Our results imply that marine secondary producers increase their respiration and feeding rate in response to ocean acidification to balance the energy cost against increased acidity and CO2 concentration.

Stable isotopes and sea surface temperature on planktic foraminifera of sediment core WIND 28K

We reconstructed the surface hydrography of the South Equatorial Current in the western Indian Ocean for the last 65,000 years using a marine sediment core record. Results show that tropical Indian Ocean temperatures resemble temperatures from Antarctic ice cores with warm and cold fluctuations synchronous with the Antarctic Cold Reversal and the Antarctic warm events A1-A4. The most likely thermal link involves Subantarctic Mode Water (SAMW) which forms north of the subpolar frontal zone and spreads northward into the Indian Ocean. This subsurface water mass is the prime suspect because of a stronger temperature response in the thermocline (recorded by the foraminifer N. dutertrei) than in surface water (G. ruber).

Surface velocity fields, digital elevation models and ice front positions derived from multi-mission SAR remote sensing data at Sjögren Inlet glaciers, Antarctic Peninsula

Substantial retreat or disintegration of numerous ice shelves have been observed on the Antarctic Peninsula. The ice shelf in the Prince Gustav Channel retreated gradually since the late 1980's and broke-up in 1995. Tributary glaciers reacted with speed-up, surface lowering and increased ice discharge, consequently contributing to sea level rise. We present a detailed long-term study (1993-2014) on the dynamic response of Sjögren Inlet glaciers to the disintegration of Prince Gustav Ice Shelf. We analyzed various remote sensing datasets to observe the reactions of the glaciers to the loss of the buttressing ice shelf. A strong increase in ice surface velocities was observed with maximum flow speeds reaching 2.82±0.48 m/d in 2007 and 1.50±0.32 m/d in 2004 at Sjögren and Boydell glaciers respectively. Subsequently, the flow velocities decelerated, however in late 2014, we still measured about two times the values of our first measurements in 1996. The tributary glaciers retreated 61.7±3.1 km² behind the former grounding line of the ice shelf. In regions below 1000 m a.s.l., a mean surface lowering of -68±10 m (-3.1 m/a) was observed in the period 1993-2014. The lowering rate decreased to -2.2 m/a in recent years. Based on the surface lowering rates, geodetic mass balances of the glaciers were derived for different time steps. High mass loss rate of -1.21±0.36 Gt/a was found in the earliest period (1993-2001). Due to the dynamic adjustments of the glaciers to the new boundary conditions the ice mass loss reduced to -0.59±0.11 Gt/a in the period 2012-2014, resulting in an average mass loss rate of -0.89±0.16 Gt/a (1993-2014). Including the retreat of the ice front and grounding line, a total mass change of -38.5±7.7 Gt and a contribution to sea level rise of 0.061±0.013 mm were computed. Analysis of the ice flux revealed that available bedrock elevation estimates at Sjögren Inlet are too shallow and are the major uncertainty in ice flux computations. This temporally dense time series analysis of Sjögren Inlet glaciers shows that the adjustments of tributary glaciers to ice shelf disintegration are still going on and provides detailed information of the changes in glacier dynamics.

Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/1, M34/2, M34/3 and M34/4

To enhance the limited information available about the palaeo-ecological significance of calcareous dinoflagellates, we have studied their lateral distribution in surface sediments of the equatorial and south Atlantic between 13°N and 36°S. Calcareous dinoflagellate cysts appear to be widely distributed throughout the studied area. In the surface sediments, concentrations (cyst per gram dry sediment) of the vegetative stage Thoracosphaera heimii are generally higher than that of the (presumably) calcareous resting cysts. Distribution patterns in surface sediments of Orthopithonella granifera (Fütterer) Keupp and Versteegh, Rhabdothorax spp. Kamptner., Sphaerodinella albatrosiana (Kamptner) Keupp and Versteegh S. albatrosiana praratabulated, Sphaerodinella tuberosa var. 1 (Kamptner) Keupp and Versteegh and S. tuberosa var. 2 and the ratios between these species have been compared with temperature, salinity, density and stratification gradients in the upper water column. Rhabdothorax spp. is characteristically present in sediments of more temperate regions characterized by high seasonality. Dinoflagellates producing these cysts are able to tolerate high nutrient concentrations, and mixing of the water column. S. albatrosiana is abundant in regions characterized by high sea surface temperatures and oligotrophic surface water conditions. In contrast, the distribution of S. tuberosa var. 2 is negatively related to temperature. The other cyst species did not show a characteristic pattern in relation to the studied environmental gradients. The ratio of Sphaerodinella tuberosa var. 2 to Orthopithonella granifera can be used for reconstructing the presence of stratification in the upper 50 m of the water column, whereas the ratios of S. tuberosa var. 2 to Sphaerodinella albatrosiana and of O. granifera to Rhabdothorax spp. might be used for palaeotemperature reconstructions. Calcareous dinoflagellate cysts are abundant in oligotrophic areas and may be useful for the reconstruction of palaeoenvironmental conditions.

Alkenones and sea surface reconstruction of sediments from, the Arabian Sea

Deep-sea sediments of two cores from the western (TY93-929/P) and the southeastern (MD900963) Arabian Sea were used to study the variations of the Indian monsoon during previous climatic cycles. Core TY93-929/P was located between the SW monsoon driven upwelling centres off Somalia and Oman, which are characterized by large seasonal sea surface temperature (SST) and particle flux changes. By contrast, core MD900963, was situated near the Maldives platform, an equatorial ocean site with a rather small SST seasonality (less than 2°C). For both cores we have reconstructed SST variations by means of the unsaturation ratio of C37 alkenones, which is compared with the delta18O records established on planktonic foraminifera. In general, the SST records follow the delta18O variations, with an SST maximum during oxygen isotope stage 5.5 (the Last Interglacial at about 120-130 kyr) and a broad SST minimum during isotope stage 4 and 3.3 (approximately 40-50 kyr). The SST difference between the Holocene and the Last Glacial Maximum (LGM) is of the order of 2°C. In both cores the SSTs during isotope stage 6 are distinctly higher by 1-2°C than the cold SST minima during the last glacial cycle (LGM and stage 3). To reconstruct qualitatively the past productivity variations for the two cores, we used the concentrations and fluxes of alkenones and organic carbon, together with a productivity index based on coccolith species (Florisphaera profunda relative abundance). Within each core, there is a general agreement between the different palaeoproductivity proxies. In the southeastern Arabian Sea (core MD900963), glacial stages correspond to relatively high productivity, whereas warm interstadials coincide with low productivity. All time series of productivity proxies are dominated by a cyclicity of about 21-23 kyr, which corresponds to the insolation precessional cycle. A hypothesis could be that the NE monsoon winds were stronger during the glacial stages, which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone. By contrast, the records are more complicated in the upwelling region of the western Arabian Sea (core TY93-929/P). This is partly due to large changes in the sedimentation rates, which were higher during specific periods (isotope stages 6, 5.4, 5.2, 3 and 2). Unlike core MD900963, no simple relationship emerges from the comparison between the delta18O stratigraphy and productivity records. The greater complexity observed for core TY93-929/P could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons, the SW monsoon being enhanced during interglacial periods, whereas the NE monsoon was increased during glacial intervals. A similar line of reasoning also could help explain the SST records by the superimposition of variations of three components: global atmospheric temperature, and SW and NE monsoon dynamics.

(Table 2) Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/2 and M34/2

The organic walled cyst content of 41 surface sediment samples from the south-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insight into which environmental factors influence the distribution of individual cyst species, the cyst associations have been compared with oceanographic characteristics of the overlying water masses, i.e. temperature, salinity, density and stratification gradients. The associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors of transport and preservation of the cysts. Five associations have been recognised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Benguela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. The factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution.

Impact of high pCO2 and warmer temperatures on the process of silica biomineralization in the sponge Mycale grandis

Siliceous sponges have survived pre-historical mass extinction events caused by ocean acidification and recent studies suggest that siliceous sponges will continue to resist predicted increases in ocean acidity. In this study, we monitored silica biomineralization in the Hawaiian sponge Mycale grandis under predicted pCO2 and sea surface temperature scenarios for 2100. Our goal was to determine if spicule biomineralization was enhanced or repressed by ocean acidification and thermal stress by monitoring silica uptake rates during short-term (48 h) experiments and comparing biomineralized tissue ratios before and after a long-term (26 d) experiment. In the short-term experiment, we found that silica uptake rates were not impacted by high pCO2 (1050 µatm), warmer temperatures (27°C), or combined high pCO2 with warmer temperature (1119 µatm; 27°C) treatments. The long-term exposure experiments revealed no effect on survival or growth rates of M. grandis to high pCO2 (1198 µatm), warmer temperatures (25.6°C), or combined high pCO2 with warmer temperature (1225 µatm, 25.7°C) treatments, indicating that M. grandis will continue to prosper under predicted increases in pCO2 and sea surface temperature. However, ash-free dry weight to dry weight ratios, subtylostyle lengths, and silicified weight to dry weight ratios decreased under conditions of high pCO2 and combined pCO2 warmer temperature treatments. Our results show that rising ocean acidity and temperature have marginal negative effects on spicule biomineralization and will not affect sponge survival rates of M. grandis.

Water temperature reconstructions based on paired Uk'37 and Tex86 records, and paired surface and subsurface Mg/Ca records

This dataset contains the collection of available published paired Uk'37 and Tex86 records spanning multi-millennial to multi-million year time scales, as well as a collection of Mg/Ca-derived temperatures measured in parallel on surface and subsurface dwelling foraminifera, both used in the analyses of Ho and Laepple, Nature Geoscience 2016. As the signal-to-noise ratios of proxy-derived Holocene temperatures are relatively low, we selected records that contain at least the last deglaciation (oldest sample >18kyr BP).

Oxygen, pH and calcium dynamics and fluxes at the thallus surface under ambient (8.1) and low (7.8) seawater pH and across a range of irradiances

Presently, an incomplete mechanistic understanding of tropical reef macroalgae photosynthesis and calcification restricts predictions of how these important autotrophs will respond to global change. Therefore, we investigated the mechanistic link between inorganic carbon uptake pathways, photosynthesis and calcification in a tropical crustose coralline alga (CCA) using microsensors. We measured pH, oxygen (O2), and calcium (Ca2+) dynamics and fluxes at the thallus surface under ambient (8.1) and low (7.8) seawater pH (pHSW) and across a range of irradiances. Acetazolamide (AZ) was used to inhibit extracellular carbonic anhydrase (CAext), which mediates hydrolysis of HCO3-, and 4,4' diisothiocyanatostilbene-2,2'-disulphonate (DIDS) that blocks direct HCO3- uptake by anion exchange transport. Both inhibited photosynthesis, suggesting both diffusive uptake of CO2 via HCO3- hydrolysis to CO2 and direct HCO3- ion transport are important in this CCA. Surface pH was raised approximately 0.3 units at saturating irradiance, but less when CAext was inhibited. Surface pH was lower at pHSW 7.8 than pHSW 8.1 in the dark, but not in the light. The Ca2+ fluxes were large, complex and temporally variable, but revealed net Ca2+ uptake under all conditions. The temporal variability in Ca2+ dynamics was potentially related to localized dissolution during epithallial cell sloughing, a strategy of CCA to remove epiphytes. Simultaneous Ca2+ and pH dynamics suggest the presence of Ca2+/H+ exchange. Rapid light-induced H+ surface dynamics that continued after inhibition of photosynthesis revealed the presence of a light-mediated, but photosynthesis-independent, proton pump. Thus, the study indicates metabolic control of surface pH can occur in CCA through photosynthesis and light-inducible H+ pumps. Our results suggest that complex light-induced ion pumps play an important role in biological processes related to inorganic carbon uptake and calcification in CCA.