61. CO2 net fluxes along south and southeast Brazilian continental shelf and slope

Ana G. Correa1, Iole B. M. Orselli1, Rodrigo Kerr1

 

1Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Av. Itália km 8, Rio Grande, 96203-900, RS, Brazil.

 

Background: Rapid increase of CO2 in the atmosphere is receiving a huge importance due to its effect on global climate, what is related to ocean absorption of this gas. Continental margins play an important role in biogeochemical cycles due to nutrient input and exchanges with atmosphere and open ocean. Studies concerning CO2 net fluxes (FCO2) in the South Atlantic Ocean are limited, mainly concentrated in punctual researches in the Patagonian shelves and one oceanographic cruise in Southeast Atlantic Ocean.

 

Methods: Continuous measurements of CO2  molar fraction (xCO2) in the seawater and atmosphere were  sampled using a GO-8050/ Li-COR LI-7000, during early spring of 2014. The cruise carried out between Rio de Janeiro and Rio Grande – Brazil (23-32°S, 43-51°W). CO2 partial pressure (pCO2) was calculated using xCO2. FCO2 was determined using wind speed of ECMWF reanalysis project and based on Takahashi et al. (2009) transfer coefficient.

 

Findings: Average pCO2sw value was (± standard deviation) 367.9 ±11 atm, with a maximum of 423.2 atm and a minimum of 333.1 atm. Mean pCO2atm was 396.7 ±

2.5 atm.  pCO2  average value was -28.75 ±11.1 atm  with a maximum of 23.7

atm and a minimum of -62.5 atm. Wind speed average value was of 34.17 ±7.1 m s-1. FCO2 average value was -87.9 ±41.8. During the cruise a senescent bloom of Trichodesmium spp was observed, with high pCO2sw  values achieving 873 atm (pCO2 of 476 atm), being the only region along the slope where CO2 was released to the atmosphere.

 

Conclusions: In almost all sampled area pCO2 and FCO2 were negative, defining this region as a CO2  sink during the early spring, agreeing with recent modelling study in the region and contrasting with previous measurements of the southeastern Brazil, that characterized the entire continental shelf as a CO2 source to the atmosphere during spring.

Quantifying the influence of CO2 seasonality on future aragonite under-saturation onset

Chair: Samantha Siedlecki

Tristan P. Sasse(1), Ben I. McNeil(2), Richard J. Matear(3), Andrew Lenton(4)

1 University of New South Wales, Sydney, NSW, Australia
2 University of New South Wales, Sydney, NSW, Australia
3 CSIRO Oceans and Atmosphere National Research Flagship, Hobart, Tasmania, Australia
4 CSIRO Oceans and Atmosphere National Research Flagship, Hobart, Tasmania, Australia

Background
Ocean acidification is a predictable consequence of rising atmospheric carbon dioxide (CO 2), and is highly likely to impact the entire marine ecosystem – from plankton at the base of the food chain to fish at the top. Factors which are expected to be impacted include reproductive health, organism growth and species composition and distribution.Predicting when critical threshold values will be reached is crucial for projecting the future health of marine ecosystems and for marine resources planning and management. The impacts of ocean acidification will be first felt at the seasonal scale, however our understanding how seasonal variability will influence rates of future ocean acidification remains poorly constrained due to current model and data limitations.

Methods
To address this issue, we first quantified the seasonal cycle of aragonite saturation state for the global open-ocean (1°×1° resolution) utilizing new data-based estimates of global ocean surface dissolved inorganic carbon and alkalinity. This seasonality was then combined with earth system model projections under different emissions scenarios (RCPs 2.6, 4.5 and 8.5) to provide new insights into future aragonite under-saturation onset.

Findings
Under a high emissions scenario (RCP 8.5), our results suggest accounting for seasonality will bring forward the initial onset of month-long under-saturation by 17±10 years compared to annual-mean estimates, with differences extending up to 35±16 years in the North Pacific due to strong regional seasonality. This earlier onset will result in large-scale under-saturation once atmospheric CO 2 reaches 496ppm in the North Pacific and 511ppm in the Southern Ocean, independent of emission scenario.
Conclusions
This work suggests accounting for seasonality is critical to projecting the future impacts of ocean acidification on the marine environment.

Coastal upwelling off Peru: Low Oxygen, Low PH, High Variability

Chair: Yuri Artioli

Graco Michelle (1), Avy Bernales (1), Carhuapoma Wilson (1, 2), Diana Alvites (2), Beaufort Luc (3), David Correa (1)

1 DGIOCC, Instituto del Mar del Perú IMARPE, Callao, 22, Perú
2 CEREGE Université Aix- Marseille. Aix., France
3 University Peruana Cayetano Heredia (UPCH), Lima, Perú

Background
The Coastal Upwelling off Perú, one of the most productive ecosystems in the world, is considered a hot spot for the scientific community, because of the extensive and intensive Oxygen Minimum Zone (ZMO), the low pH, its role as a source of CO2 and N2O and one of the strongest interannual signals of variability such as El Niño. Considering the complex relationships between environmental factors, biotic components and variability it was necessary develop an integrated study with different disciplines and approaches in order to get a better understanding of how this ecosystem works and the feedbacks between its different components.

Methods
Since 2013, at IMARPE, we perform a national project with international partners to investigate the upwelling of Peru from the sediments to the atmosphere. We perform with a bimonthly resolution a sampling in the central area of Peru, Callao (12°C) from the coast to 50 mn, in order to characterize the physical, chemical and the biological component.

Findings
Here, we will present recent results associated with the last El Niño event 2014-2015 in the variability of the OMZ and pH off Callao and the strong impact in the chemistry and the phytoplankton communities. The data indicate a strong presence of the nanoplankton community and coccolitophorids with different degrees of calcification in a coastal open-ocean gradient of physical conditions, oxygen, N/P ratio and pH.

Conclusions
We confirm that the upwelling ecosystems is a window for insights in the context of the climate change and is necessary the review of some paradigms.

Ocean acidification in the Weddell Sea: Upwelling and ice cover

Chair: Joellen Russell

Mario Hoppema(1), Steven van Heuven(2), Rob Middag(3) , Kim Currie(4) , Oliver Huhn(5)

1 Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, 27515, Germany
2 Netherlands Institute for Sea Research, Texel, the Netherlands
3 Dept. of Chemistry, NIWA/University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand
4 NIWA / University of Otago Research Centre for Oceanography, Dunedin, 9054, New Zealand
5 Institute of Environmental Physics, University of Bremen, Bremen, 28359, Germany

Methods

Using a suite of cruises spanning several decades, we investigated the time rate of change of Total CO2 (TCO2) and related variables in the surface layer of the Weddell Gyre and adjacent Antarctic Circumpolar Current.

 

Findings

At the Prime Meridian, a significant TCO2 increase was observed, which is clear evidence for the invasion of anthropogenic CO2. In the Weddell Sea Bottom Water at this location, the spatial distribution of the increase in TCO2 bears a high resemblance to that of CFCs, suggesting that the changes in TCO2 have been propagated from the surface. However, other variables like dissolved oxygen and silicate also show trends through time, pointing to non-steady state conditions which might also affect the derived CO2 increase. Near the tip of the Peninsula, the coldest and most recently ventilated waters, hugging the continental slope, exhibit increasing TCO2 over time despite the presence of sea ice.

 

Conclusions

This indicates that CO2 uptake and acidification occur although sea ice cover is present for a significant period of the year. The CO2 increases/changes were translated into changes of carbonate ion and pH. Additionally, we show data on the partial pressure of CO2 for the Weddell Sea, in particular on the seasonal cycle and the saturation state. We determined seasonal changes in CO2, i.e., drawdown through phytoplankton, which we compared to seasonal changes in trace metals in this region.

 

Seasonal change in ocean acidification state in Kongsfjorden: implications for calcifying organisms

Chair: Yuri Artioli

Melissa Chierici(1), Agneta Fransson(2), Haakon Hop(2), Helen Findlay(3), Svein Kristiansen(4), Vladmir Pavlov(2), Anette Wold(2)
1 Institute of Marine Research and FRAM-High North Centre of Climate and the Environment, Tromsø, 9294 Norway

2 Norwegian Polar Institute, Fram Centre, Tromsø 9296, Norway
3 Plymouth Marine Laboratory, Southampton, UK
4 UiT- The Arctic University of Norway, Tromsø, Norway

Background
Kongsfjorden is a fjord in West Spitsbergen and has no pronounced sill which makes it influenced by warm and saline Atlantic water inflow. The two retreating glaciers add freshwater to the water which also affects the ocean acidification state such as the calcium carbonate (CaCO3) saturation. By investigating the seasonal change in ocean acidification state and biogeochemical properties from winter-to-summer in two years we investigate the strength and effect of freshwater and photosynthesis on the carbonate system.

Methods
Water samples from April (winter) and July (summer) in 2013 and 2014 were collected in the water column from the glacier front to the outer shelf. The samples were analysed either directly onboard the RV Lance or were preserved for post-cruise analysis in laboratory. Samples were determined for total dissolved inorganic carbon (CT or DIC), total alkalinity (AT) and nutrient concentrations, and we calculated the full carbonate system including pH, CaCO3 saturation, fCO2 using chemical speciation models. Published data on the effect on calcifiers such as Limacina helicina at different CaCO3 saturation levels were compared with the observed saturation states in Kongsfjorden.

Findings
We found large differences between the winter and summer data entailing higher salinity and fugacity/partial pressure of CO2 (fCO2/pCO2) in winter and lower pH, compared to the summer values.

Conclusions
In winter, calcium carbonate (CaCO3) saturation (Ω) was approximately 1.6, reaching values for first signs of shell dissolution of aragonite-forming organisms such as pteropods (W<1.4). Biological CO2 consumption mitigated partly the decrease in Ω due to freshening, similar to what we found in other fjords.

Chemical and Biological Impacts of ocean acidification Along the West Coast of North America

Chair: James Orr

Richard A. Feely (a)*, Simone Alin (a), Brendan Carter (b), and Nina Bednaršek (c)

a NOAA Pacific Marine Environmental Laboratory, 7600 Sand Point Way NE, Seattle, WA 98115, USA
b Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA 98195, USA
c School of Marine and Environmental Affairs, University of Washington, Seattle, WA 98195, USA

Background
The continental shelf region off the Washington-Oregon-California coast is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO2-rich waters that can negatively impact juvenile and adult pteropods.

Methods
Seawater upwelling along the continental shelf of the west coast of North America comes from the thermocline waters of the North Pacific Gyre at depths between 150 and 300 m. Here we adapt the linear regression approach to utilize the GO-SHIP Repeat Hydrography data from the northeast Pacific to establish an annually updated relationship between the anthropogenic carbon (Canth) and potential density. This relationship was then used with the NOAA Ocean Acidification Program West Coast Ocean Acidification (WCOA) cruise data sets from 2007, 2011, 2012, and 2013 to determine the spatial variations of Canth along the coast.

Findings
Our results show large spatial differences in Canth in surface waters along the coast, with the lowest values in strong upwelling regions off northern California and southern Oregon and higher values to the north and south of this region. Coastal dissolved inorganic carbon concentrations are also elevated due to a natural respiration process. Average surface Canth more than doubles the surface respiration component. In contrast, Canth is only ~1/3rd and ~1/5th of the remineralized component at 50 m and 100 m depth, respectively. The Canth plays a significant role in causing the dissolution of pteropod shells in onshore and offshore waters.

Conclusions
Uptake of Canth has caused the aragonite saturation horizon to shoal by approximately 30–50 m since the preindustrial period so that undersaturated waters are well within the regions of the continental shelf that affect the dissolution of living pteropod shells. Our data shows that the most severe biological impacts occur in the onshore waters where corrosive waters are closest to the surface.

Sensitivity of Future ocean acidification to Land carbon uptake

Chair: Joellen Russell

Richard Matear (1), Andrew Lenton (1)

1 CSIRO, Hobart, Tasmania, Australia

Background
The future land carbon uptake under the various emission scenarios is highly uncertain 1, 2 with the potential to significantly impact future climate change projections 3. Previous studies have focus on how the land carbon uptake may impact the future climate 4 but by modifying the atmospheric CO2 concentrations the land uptake will also influence the future trajectory for ocean acidification. Ocean acidification (OA) has the potential to significantly impact marine ecosystem by reducing calcifications rates 5, altering phytoplankton composition6, changing fish behaviour7 and affecting larval recruitment8.

Methods
Making accurate projection of ocean acidi- fication is essential to assessing the future impact of ocean acidification. Here, we use the CO2 emissions scenarios for 4 Representative Concentration Pathways (RCPs) with an Earth Sys- tem Model to project the future trajectory of ocean acidification.

Findings
We show that simulated response on the land carbon uptake has a significant impact on the onset of under-saturated conditions in the Southern Ocean and Arctic Ocean, the suitable habitat for tropical coral and the deepwater saturation state. The impact is most significant for the middle emission scenario (RCP4.5) when the time negative ocean acidification condition is advanced.

Conclusions
• rate of OA related to land carbon uptake (climate-carbon feedback)

• sensitivity is largest for the middle emissions scenarios (RCP4.5 and 6) and could accelerate the impact of ocean acidification. Such acceleration increases OA impacts but perhaps it will also undermine the ability of marine biota to adapt to the changing environment

• need to do ESM simulations to make future OA projections (relevance to AR6) and reduce the uncertainty in the climate-carbon feedback

References
1.Zhang, Q., Wang, Y. P., Matear, R. J., Pitman, A. J. & Dai, Y. J. Nitrogen and phosphorous limitations significantly reduce future allowable CO2 emissions. Geophysical Research Letters (2014).

2.Wenzel, S., Cox, P. M., Eyring, V. & Friedlingstein, P. Emergent constraints on climatecar- bon cycle feedbacks in the CMIP5 Earth system models. Journal of Geophysical Research- Biogeosciences (2014).

3.Zaehle, S., Friedlingstein, P. & Friend, A. D. Terrestrial nitrogen feedbacks may accelerate future climate change. Geophysical Research Letters 37, L01401 (2010).

4.Friedlingstein, P. et al. Climate-carbon cycle feedback analysis: Results from the C4MIP 11 model intercomparison. J Climate 19, 3337–3353 (2006).

5.Stojkovic, S., Beardall, J. & Matear, R. J. CO2concentrating mechanisms in three southern hemisphere strains of Emiliania huxleyi. Journal Of Phycology 49, 670–679 (2013).

6.Lohbeck, K. T., Riebesell, U. & Reusch, T. B. H. Adaptive evolution of a key phytoplankton species to ocean acidification. Nature Geoscience 5, 346–351 (2012).

7.Munday, P. et al. Ocean acidification impairs olfactory discrimination and homing ability of a marine fish. Proceedings Of The National Academy Of Sciences Of The United States Of America 106, 1848–1852 (2009).

Ross, P. M., Parker, L., O’connor, W. A. & Bailey, E. A. The Impact of Ocean Acidification on Reproduction, Early Development and Settlement of Marine Organisms. Water 3, 1005–1030 (2011).

Variability of oceanic carbon cycling and its relation to the ocean acidification in the North Pacific Ocean

Chair: Joellen Russell

Fei Chai (1) and Peng Xiu (2)
1School of Marine Sciences, University of Maine, Orono, ME, USA. E-mail: fchai@maine.edu
1State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China

The ocean plays an important role in regulating global carbon cycle by taking up and releasing carbon dioxide (CO2) from and to the atmosphere simultaneously. The ocean has absorbed about 50% of CO2 emitted to the atmosphere by fossil fuel burning, and this ability has been suggested to continue at a relatively stable rate of 1.4- 1.8 PgC per year. The direct impact of ocean absorbing CO2 is leading to the ocean acidification (OA) that can affect biological activities and the oceanic CO2 system. Here, we propose a coupled three-dimensional modeling study to investigate the dynamics of the carbonate system in the North Pacific Ocean, based on the Regional Ocean Modeling System (ROMS) and the biogeochemical model, CoSiNE model, along with a carbonate system. The model results are compared and constrained with available in-situ measurements all over the Pacific Ocean. Further analysis of the model results indicates that the carbonate system in the North Pacific Ocean has strong spatial and temporal variations in terms of sea p CO2, pH, and the aragonite saturation state. Long-term trends of these variables show conspicuous spatial variability that could be related to the local physical and biogeochemical conditions. We also analyze the impacts and feedbacks of OA to the sea p CO2 and sea-air CO2 flux. This modeling study allows us to look into the detailed mechanisms in regulating oceanic carbonate system with high spatial and temporal resolutions that field observations normally cannot provide.

Changes in ocean acidification evaluated in the southern Indian ocean from observations over the last 30 years

Chair: Kumiko Azetsu-Scott

Renaud Gomez (1)*, Claire Lo Monaco (1), Nicolas Metzl (1)

1 Sorbonne Universités (UPMC, Univ Paris 06)-CNRS-IRD-MNHN, LOCEAN Laboratory, 4 place Jussieu, Paris, 75005, France

Background
The Southern Ocean is an important sink for anthropogenic CO2 and a region of Subantarctic Mode Water (SAMW) formation. This results in a large accumulation of anthropogenic carbon (Cant) in the ocean between 30°S and 50°S, which leads to a decrease in seawater pH. This acidification process could impact marine organism, the biological carbon pump and thus global climate.

Methods
We used total alkalinity (TA) and dissolved inorganic carbon (DIC) measurements collected during 10 oceanographic cruises in the Southern Indian Ocean from 1985 to 2012 to estimate the decadal trends in pH and the saturation state for aragonite in the Antarctic and Subantarctic surface waters (ASW and SASW respectively) and also in the SAMW. We also identify the different drivers behind the observed trends.

Findings
Over this period, the aragonite saturation state decrease is much higher in the SASW (0.20±0.07/decade) than in the SAMW and the ASW (0.09±0.02/decade) due to a maximum increase of DIC. Concerning the pH the observed decrease is statistically similar in the three studied waters (from 0.018±0.005/decade to 0.025±0.003/decade). In the SASW and the SAMW the pH decrease is mainly attributed to a DIC increase, whereas in the ASW interannual changes of carbon parameters play a significant role.

Conclusions
Over the last 30 years significant pH and aragonite decrease were observed in the three studied waters. The role of natural variability or climate-induced changes in the carbonate chemistry need to be better understood for future estimations of ocean acidification parameters

The exposure of the Great Barrier Reef to ocean acidification

Chair: James Orr

Mathieu Mongin(1), Mark E. Baird (1), Bronte Tilbrook (1, 2), Richard J. Matear (1), Andrew Lenton (1), Mike Herzfeld (1), Karen A. Wild-Allen (1), Jenny Skerratt (1), Nugzar Margvelashvili (1), Barbara J. Robson (3), Carlos M. Duarte (4), Malin S. M. Gustafsson (5), Peter J. Ralph (5), Andrew D. L. Steven (1)

1 CSIRO Oceans and Atmosphere Flagship, Hobart, Australia
2 Antarctic Climate and Ecosystems Co-operative Research Centre, Hobart, Australia
3 CSIRO Land and Water Flagship, Canberra, Australia
4 Red Sea Research Center, King Abdullah University of Science and Technology, Kingdom of Saudi Arabia
5 Plant Functional Biology and Climate Change Cluster (C3), Faculty of Science, University of Technology Sydney, Australia

The Great Barrier Reef (GBR), one of the world’s iconic marine ecosystems, is founded on reef-building corals1. Corals typically build their exoskeleton with aragonite – a crystalised form of calcium carbonate – but ocean acidification is lowering the pH and aragonite saturation state of seawater (Ωa)2. The downscaling of ocean acidification projections from the global scale to the GBR requires that the diverse set of coastal-shelf-open ocean drivers controlling Ωa be resolved3. In a novel approach, we used observations4 and a hindcast of a regional coupled circulation–biogeochemical model to estimate the mean Ωa experienced by 3,581 individual reefs of the GBR, and to apportion the relative contributions of the hydrological cycle, regional hydrodynamics and metabolism on Ωa variability. The coupled model shows a clear spatial structure in Ωa, with large gradients across and along the GBR shelf. We find more detail, and a greater range (1.43), than found in previously-compiled coarse model-generated maps of Ωa of the region (0.4)5, or in sparse observations (0.51)4. Most of the variability in Wa was due processes occurring upstream of the reef in question. By quantifying the relationship between the open-ocean and the GBR we see that the critical thresholds for coral health are likely to be passed sooner than currently projected by the IPCC assessment report.

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