Posts Tagged 'field'

Seasonal variability of carbonate chemistry and decadal changes in waters of a marine sanctuary in the Northwestern Gulf of Mexico

Highlights

• Temperature dominated seawater carbonate system variations in FGBNMS.
• Subsurface acidification is caused by anthropogenic CO2 uptake and higher respiration.
• The FGBNMS is currently a negligible atmospheric CO2 sink.

Abstract

We report seasonal water column carbonate chemistry data collected over a three-year period (late 2013 to 2016) at Flower Garden Banks National Marine Sanctuary (FGBNMS) located on the subtropical shelf edge of the northwestern Gulf of Mexico. The FGBNMS hosts the northernmost tropical coral species in the contiguous United States, with over 50% living coral cover. Presented here are results from samples of the upper 25 m of the water column collected from September 2013 to November 2016. Additionally, following a localized mortality event likely associated with major continental flooding in summer 2016, water samples from up to ~250 m depth were collected in the broader FGBNMS area on a rapid response cruise to examine the seawater carbonate system. Both surface (<5 m) total alkalinity (TA) and total dissolved inorganic carbon (DIC) vary over small ranges (2391 ± 19 μmol kg−1 and 2060 ± 19 μmol kg−1, respectively) for all times-series samples. Temperature and salinity both played an important role in controlling the surface water carbonate system dynamics, although temperature was the sole significant factor when there was no flooding. The FGBNMS area acted as a sink for atmospheric CO2 in winter and a CO2 source in summer, while the time-integrated CO2 flux is close to zero (−0.14 ± 1.96 mmol-C m−2 yr−1). Results from three cruises, i.e., the Gulf of Mexico and East Coast Carbon Project (GOMECC-1) in 2007, the rapid response study, and the Gulf of Mexico Ecosystems and Carbon Cruise (GOMECC-3), revealed decreases in both pH and saturation state with respect to aragonitearag) in subsurface waters (~100–250 m) over time. These decreases are larger than those observed in other tropical and subtropical waters. Based on reaction stoichiometry, calculated anthropogenic CO2 contributed 30–41% of the overall DIC increase, while elevated respiration accounted for the rest.

Continue reading ‘Seasonal variability of carbonate chemistry and decadal changes in waters of a marine sanctuary in the Northwestern Gulf of Mexico’

Does nutrient availability regulate seagrass response to elevated CO2?

Future increases in oceanic carbon dioxide concentrations (CO2(aq)) may provide a benefit to submerged plants by alleviating photosynthetic carbon limitation. However, other environmental factors (for example, nutrient availability) may alter how seagrasses respond to CO2(aq) by regulating the supply of additional resources required to support growth. Thus, questions remain in regard to how other factors influence CO2(aq) effects on submerged vegetation. This study factorially manipulated CO2(aq) and nutrient availability, in situ, within a subtropical seagrass bed for 350 days, and examined treatment effects on leaf productivity, shoot density, above- and belowground biomass, nutrient content, carbohydrate storage, and sediment organic carbon (Corg). Clear, open-top chambers were used to replicate CO2(aq) forecasts for the year 2100, whereas nutrient availability was manipulated via sediment amendments of nitrogen (N) and phosphorus (P) fertilizer. We provide modest evidence of a CO2 effect, which increased seagrass aboveground biomass. CO2(aq) enrichment had no effect on nutrient content, carbohydrate storage, or sediment Corg content. Nutrient addition increased leaf productivity and leaf N content, however did not alter above- or belowground biomass, shoot density, carbohydrate storage, or Corg content. Treatment interactions were not significant, and thus NP availability did not influence seagrass responses to elevated CO2(aq). This study demonstrates that long-term carbon enrichment may alter the structure of shallow seagrass meadows, even in relatively nutrient-poor, oligotrophic systems.

Continue reading ‘Does nutrient availability regulate seagrass response to elevated CO2?’

The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river (update)

Ocean acidification threatens to reduce pH and aragonite saturation state (ΩA) in estuaries, potentially damaging their ecosystems. However, the impact of highly variable river total alkalinity (TA) and dissolved inorganic carbon (DIC) on pH and ΩA in these estuaries is unknown. We assess the sensitivity of estuarine surface pH and ΩA to river TA and DIC using a coupled biogeochemical model of the Strait of Georgia on the Canadian Pacific coast and place the results in the context of global rivers. The productive Strait of Georgia estuary has a large, seasonally variable freshwater input from the glacially fed, undammed Fraser River. Analyzing TA observations from this river plume and pH from the river mouth, we find that the Fraser is moderately alkaline (TA 500–1000 µmol kg−1) but relatively DIC-rich. Model results show that estuarine pH and ΩA are sensitive to freshwater DIC and TA, but do not vary in synchrony except at high DIC : TA. The asynchrony occurs because increased freshwater TA is associated with increased DIC, which contributes to an increased estuarine DIC : TA and reduces pH, while the resulting higher carbonate ion concentration causes an increase in estuarine ΩA. When freshwater DIC : TA increases (beyond  ∼  1.1), the shifting chemistry causes a paucity of the carbonate ion that overwhelms the simple dilution/enhancement effect. At this high DIC : TA ratio, estuarine sensitivity to river chemistry increases overall. Furthermore, this increased sensitivity extends to reduced flow regimes that are expected in future. Modulating these negative impacts is the seasonal productivity in the estuary which draws down DIC and reduces the sensitivity of estuarine pH to increasing DIC during the summer season.

Continue reading ‘The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river (update)’

Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut

Highlights

  • Total bivalve community composition influenced by grain size, pH, alkalinity, and date
  • Short term drivers of bivalve community settlement influenced by carbonate chemistry parameters
  • Different bivalve species respond to different carbonate chemistry cues for settlement.

Abstract

Cues that drive bivalve settlement and abundance in sediments are not well understood, but recent reports suggest that sediment carbonate chemistry may influence bivalve abundance. In 2013, we conducted field experiments to assess the relationship between porewater sediment carbonate chemistry (pH, alkalinity (At), dissolved inorganic carbon (DIC)), grain size, and bivalve abundance throughout the July–September settlement period at two sites in Long Island Sound (LIS), CT. Two dominate bivalves species were present during the study period Mya arenaria and Nucula spp. Akaike’s linear information criterion models, indicated 29% of the total community abundance was predicted by grain size, salinity, and pH. When using 2 weeks of data during the period of peak bivalve settlement, pH and phosphate concentrations accounted 44% of total bivalve community composition and 71% of Nucula spp. abundance with pH, phosphate, and silica. These results suggest that sediment carbonate chemistry may influence bivalve abundance in LIS.

Continue reading ‘Variability in sediment-water carbonate chemistry and bivalve abundance after bivalve settlement in Long Island Sound, Milford, Connecticut’

Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon

In situ production responses of air-exposed intertidal communities under CO2 enrichment are reported here for the first time. We assessed the short-term effects of CO2 on the light responses of the net community production (NCP) and community respiration (CR) of intertidal Z. noltei and unvegetated sediment communities of Ria Formosa lagoon, when exposed to air. NCP and CR were measured in situ in summer and winter, under present and CO2 enriched conditions using benthic chambers. Within chamber CO2 evolution measurements were carried out by a series of short-term incubations (30 min) using an infra-red gas analyser. Liner regression models fitted to the NCP-irradiance responses were used to estimate the seasonal budgets of air-exposed, intertidal production as determined by the daily and seasonal variation of incident photosynthetic active radiation. High CO2 resulted in higher CO2 sequestration by both communities in both summer and winter seasons. Lower respiration rates of both communities under high CO2 further contributed to a potential negative climate feedback, except in winter when the CR of sediment community was higher. The light compensation points (LCP) (light intensity where production equals respiration) of Z. noltei and sediment communities also decreased under CO2 enriched conditions in both seasons. The seasonal community production of Z. noltei was 115.54 ± 7.58 g C m−2 season−1 in summer and 29.45 ± 4.04 g C m−2 season−1 in winter and of unvegetated sediment was 91.28 ± 6.32 g C m−2 season−1 in summer and 25.83 ± 4.01 g C m−2 season−1 in winter under CO2 enriched conditions. Future CO2 conditions may increase air-exposed seagrass production by about 1.5-fold and unvegetated sediments by about 1.2-fold.

Continue reading ‘Short term CO2 enrichment increases carbon sequestration of air-exposed intertidal communities of a coastal lagoon’

Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages

Increasing atmospheric carbon dioxide and its dissolution in seawater have reduced ocean pH and carbonate ion concentration with potential implications to calcifying organisms. To assess the response of Caribbean benthic foraminifera to low carbonate saturation conditions, we analyzed benthic foraminifera abundance and relative distribution in proximity to low carbonate saturation submarine springs and at adjacent control sites. Our results show that the total abundance of benthic foraminifera is significantly lower at the low pH low calcite saturation submarine springs than at control sites, despite higher concentrations of inorganic carbon at the spring sites. The relative abundance of symbiont-bearing foraminifera and agglutinated foraminifera was higher at the low pH low calcite saturation submarine springs compared to control sites. These differences indicate that non-symbiont bearing heterotrophic calcareous foraminifera are more sensitive to the effects of ocean acidification than non-calcifying and symbiont bearing foraminifera, suggesting that future ocean acidification may impact natural benthic foraminifera populations.

Continue reading ‘Impact of carbonate saturation on large Caribbean benthic foraminifera assemblages’

Technical note: continuous fluorescence-based monitoring of seawater pH in situ (update)

Electrical conductivity (salinity), temperature and fluorescence-based measurements of pH were employed to examine diel fluctuations in seawater carbonate chemistry of surface waters in Sydney Harbour over two multiple-day periods. A proof-of-concept device employing the fluorescence-based technique provided a useful time series for pH. Alkalinity with pH and temperature were used to calculate the degree of calcite and aragonite saturation (ΩCa and ΩAr, respectively). Alkalinity was determined from a published alkalinity–salinity relationship. The fluctuations observed in pH over intervals of minutes to hours could be distinguished from background noise. While the stated phase angle resolution of the lifetime fluorometer translated into pH units was ±0.0028 pH units, the repeatability standard deviation of calculated pH was 0.007 to 0.009. Diel variability in pH, ΩAr and ΩCa showed a clear pattern that appeared to correlate with both salinity and temperature. Drift due to photodegradation of the fluorophore was minimized by reducing exposure to ambient light. The ΩCa and ΩAr fluctuated on a daily cycle. The net result of changes in pH, salinity and temperature combined to influence seawater carbonate chemistry. The fluorescence-based pH monitoring technique is simple, provides good resolution and is unaffected by moving parts or leaching of solutions over time. The use of optics is pressure insensitive, making this approach to ocean acidification monitoring well suited to deepwater applications.

Continue reading ‘Technical note: continuous fluorescence-based monitoring of seawater pH in situ (update)’


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Ocean acidification in the IPCC AR5 WG II

OUP book