Posts Tagged 'field'

Aragonite saturation state in a tropical coastal embayment dominated by phytoplankton blooms (Guanabara Bay – Brazil)

Highlights

  • The spatio-temporal variations of Ωarag were studied in a highly polluted coastal embayment.
  • High values of Ωarag were prevalent in surface waters dominated by phytoplankton blooms.
  • Lowest values of Ωarag were restricted to poorly buffered waters that receive direct effluent discharges.
  • Variations of Ωarag related to biological processes override those related to the atmospheric CO2.

Abstract

The dynamics of the aragonite saturation state (Ωarag) were investigated in the eutrophic coastal waters of Guanabara Bay (RJ-Brazil). Large phytoplankton blooms stimulated by a high nutrient enrichment promoted the production of organic matter with strong uptake of dissolved inorganic carbon (DIC) in surface waters, lowering the concentrations of dissolved carbon dioxide (CO2aq), and increasing the pH, Ωarag and carbonate ion (CO32 ), especially during summer. The increase of Ωarag related to biological activity was also evident comparing the negative relationship between the Ωarag and the apparent utilization of oxygen (AOU), with a very close behavior between the slopes of the linear regression and the Redfield ratio. The lowest values of Ωarag were found at low-buffered waters in regions that receive direct discharges from domestic effluents and polluted rivers, with episodic evidences of corrosive waters (Ωarag < 1). This study showed that the eutrophication controlled the variations of Ωarag in Guanabara Bay.

Continue reading ‘Aragonite saturation state in a tropical coastal embayment dominated by phytoplankton blooms (Guanabara Bay – Brazil)’

Multidecadal fCO2 increase along the United States southeast coastal margin

Coastal margins could be hotspots for acidification due to terrestrial-influenced CO2 sources. Currently there are no long-term (>20 years) records from biologically important coastal environments that could demonstrate sea surface CO2 fugacity (fCO2) and pH trends. Here, multi-decadal fCO2 trends are calculated from underway and moored time series observations along the United States southeast coastal margin, also referred to as the South Atlantic Bight (SAB). fCO2 trends across the SAB, derived from ∼26 years of cruises and ∼9.5 years from a moored time series, range from 3.0 to 4.5 µatm y−1, and are greater than the open ocean increases. The pH decline related to the fCO2 increases could be as much as -0.004 y−1; a rate greater than that expected from atmospheric-influenced pH alone. We provide evidence that fCO2 increases and pH decreases on an ocean margin can be faster than those predicted for the open ocean from atmospheric influence alone. We conclude that a substantial fCO2 increase across the marginal SAB is due to both increasing temperature on the middle and outer shelves, but to lateral land-ocean interactions in the coastal zone and on inner shelf.

Continue reading ‘Multidecadal fCO2 increase along the United States southeast coastal margin’

Natural ocean acidification at Papagayo upwelling system (North Pacific Costa Rica): implications for reef development

Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the upwelling season 2009. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive inter- and intra-seasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH = 7.8, pCO2 = 643.5 µatm), unveiling that natural acidification occurs sporadically also in non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification, and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During non-upwelling season, the aragonite saturation state (Ωa) rises to values of > 3.3 and enhances calcification. Aragonite saturation state values during upwelling season falls below 2.5, hampering calcification and coral growth. Low reef accretion in Bahía Culebra indicates high erosion rates and that these reefs grow on the verge of their ecological tolerance. The Ωa threshold values for coral growth, derived from the correlation between Ωa and coral linear extension rates, suggest that future ocean acidification will threaten reefs in Bahía Culebra. These data contribute to build a better understanding of the carbonate system dynamics and coral reefs key response (e.g. coral growth) to natural low-pH conditions, in upwelling areas in the Eastern Tropical Pacific and beyond.

Continue reading ‘Natural ocean acidification at Papagayo upwelling system (North Pacific Costa Rica): implications for reef development’

Environmental controls on modern scleractinian coral and reef-scale calcification

Modern reef-building corals sustain a wide range of ecosystem services because of their ability to build calcium carbonate reef systems. The influence of environmental variables on coral calcification rates has been extensively studied, but our understanding of their relative importance is limited by the absence of in situ observations and the ability to decouple the interactions between different properties. We show that temperature is the primary driver of coral colony (Porites astreoides and Diploria labyrinthiformis) and reef-scale calcification rates over a 2-year monitoring period from the Bermuda coral reef. On the basis of multimodel climate simulations (Coupled Model Intercomparison Project Phase 5) and assuming sufficient coral nutrition, our results suggest that P. astreoides and D. labyrinthiformis coral calcification rates in Bermuda could increase throughout the 21st century as a result of gradual warming predicted under a minimum CO2 emissions pathway [representative concentration pathway (RCP) 2.6] with positive 21st-century calcification rates potentially maintained under a reduced CO2 emissions pathway (RCP 4.5). These results highlight the potential benefits of rapid reductions in global anthropogenic CO2 emissions for 21st-century Bermuda coral reefs and the ecosystem services they provide.

Continue reading ‘Environmental controls on modern scleractinian coral and reef-scale calcification’

How fast is the Patagonian shelf-break acidifying?

Highlights

• Carbonate system has been driven by dilution/evaporation and sea–air CO2 exchanges.
• The Patagonian shelf is a key area of anthropogenic carbon uptake.
• SACW is acidifying faster in the Patagonian shelf-break than in the South Atlantic.
• AAIW is under risk for aragonite undersaturation near the Patagonian shelf-break.

Abstract

Anthropogenic carbon (Cant) concentration is determined according to the TrOCA method, from carbonate system data and hydrographic parameters collected during two consecutive spring cruises (2007 and 2008) in the Argentinean Patagonian shelf-break zone between 36°S and 50°S. Cant has intruded the water column until intermediate depths, with no Cant below 1000 m, in the deeper waters (i.e., North Atlantic Deep Water and Antarctic Bottom Water) of the Northern sector of the study area (i.e., North of 38°S). The higher Cant concentration is observed in Subantarctic Shelf Water in the Southern region, whereas in the Northern sector both Tropical Water and South Atlantic Central Water are equally affected by Cant intrusion. The Antarctic Intermediate Water represents the depth-limit achieved by Cant penetration, reinforcing the role that this water mass plays as an important vehicle to transport Cant to the oceans interior. The estimated Cant average (± method precision) is 46.6 ± 5.3 μmol kg− 1, considering the full depth of the water column. The ocean acidification state (ΔpH) shows an average (± standard deviation) of − 0.11 ± 0.05, thus, indicating an annual pH reduction of − 0.0010 yr− 1 since the Industrial Revolution (c.a. 1750). The degree of aragonite saturation is lowered towards undersaturation levels of calcite. The Patagonian shelf and shelf-break zones—a strong CO2 sink region in the global ocean—are likely a key area for Cant intrusion in the southwestern South Atlantic Ocean.

Continue reading ‘How fast is the Patagonian shelf-break acidifying?’

Total alkalinity and pH in the Black Sea waters in 2010 – 2011

Based on the data of the expeditionary researches of Marine Hydrophysical Institute in 2010-2011, the total alkalinity TA and pH distributions in the Black Sea waters including the Danube estuary region and the changes in the TA vertical distribution since 1988 are analyzed. It is shown that the coastal and deep-sea water TA is strongly influenced by the river flow. In the Black Sea aerobic zone, TA does not change virtually with depth and does not depend on pH. In the anaerobic zone, it weakly depends on pH, but its dependence on the hydrogen sulfide concentration is of a linear character. Comparison with the data obtained in 1988 shows that in course of the last 20 years no noticeable changes in the TA values in the Black Sea aerobic and anaerobic zones took place, whereas on the sulfide zone upper boundary the total alkalinity increased by 0.04 mg-eq*l-1.

Continue reading ‘Total alkalinity and pH in the Black Sea waters in 2010 – 2011’

The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt (update)

The Great Calcite Belt (GCB) of the Southern Ocean is a region of elevated summertime upper ocean calcite concentration derived from coccolithophores, despite the region being known for its diatom predominance. The overlap of two major phytoplankton groups, coccolithophores and diatoms, in the dynamic frontal systems characteristic of this region provides an ideal setting to study environmental influences on the distribution of different species within these taxonomic groups. Samples for phytoplankton enumeration were collected from the upper mixed layer (30 m) during two cruises, the first to the South Atlantic sector (January–February 2011; 60° W–15° E and 36–60° S) and the second in the South Indian sector (February–March 2012; 40–120° E and 36–60° S). The species composition of coccolithophores and diatoms was examined using scanning electron microscopy at 27 stations across the Subtropical, Polar, and Subantarctic fronts. The influence of environmental parameters, such as sea surface temperature (SST), salinity, carbonate chemistry (pH, partial pressure of CO2 (pCO2), alkalinity, dissolved inorganic carbon), macronutrients (nitrate + nitrite, phosphate, silicic acid, ammonia), and mixed layer average irradiance, on species composition across the GCB was assessed statistically. Nanophytoplankton (cells 2–20 µm) were the numerically abundant size group of biomineralizing phytoplankton across the GCB, with the coccolithophore Emiliania huxleyi and diatoms Fragilariopsis nana, F. pseudonana, and Pseudo-nitzschia spp. as the most numerically dominant and widely distributed. A combination of SST, macronutrient concentrations, and pCO2 provided the best statistical descriptors of the biogeographic variability in biomineralizing species composition between stations. Emiliania huxleyi occurred in silicic acid-depleted waters between the Subantarctic Front and the Polar Front, a favorable environment for this species after spring diatom blooms remove silicic acid. Multivariate statistics identified a combination of carbonate chemistry and macronutrients, covarying with temperature, as the dominant drivers of biomineralizing nanoplankton in the GCB sector of the Southern Ocean.

Continue reading ‘The influence of environmental variability on the biogeography of coccolithophores and diatoms in the Great Calcite Belt (update)’


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Ocean acidification in the IPCC AR5 WG II

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