Ecosystem Science & Modeling

Permanent URI for this communityhttps://hdl.handle.net/1969.6/89063

Browse

Now showing 1 - 20 of 31

Alkalinity distribution in the western North Atlantic Ocean margins
(2010-08-13) Cai, Wei-Jun; Hu, Xinping; Huang, Wei-Jen; Jiang, Li-Qing; Wang, Yongchen; Peng, Tsung-Hung; Zhang, Xin
Total alkalinity (TA) distribution and its relationship with salinity (S) along the western North Atlantic Ocean (wNAO) margins from the Labrador Sea to tropical areas are examined by this study. Based on the observed TA-S patterns, the mixing process that control alkalinity distribution in these areas can be categorized into a spectrum of patterns that are bracketed by two extreme mixing types, i.e., alongshore current dominated and river-dominated. Alongshore current-dominated mixing processes exhibit a segmented mixing line with a shared mid-salinity end-member. In such cases (i.e., Labrador Sea, Gulf of Maine, etc.), the y-intercept of the high salinity segment of the mixing line is generally higher than the local river alkalinity values, and it reflects the mixing history of the alongshore current. In contrast, in river-dominated mixing (Amazon River, Caribbean Sea, etc.), good linear relationships between alkalinity and salinity are generally observed, and the zero salinity intercepts of the TA-S regressions roughly match those of the regional river alkalinity values. TA-S mixing lines can be complicated by rapid changes in the river end-member value and by another river nearby with a different TA value (e.g., Mississippi-Atchafalaya/Gulf of Mexico). In the wNAO margins, regression intercepts and river end-member vale have a clear latitudinal distribution pattern, increasing from a low of ~300 mol kg-1 in the Amazon River plume to a high value between ~500-1100 mol kg-1 in the middle and high latitude margins. The highest value of ~2400 mol kg-1 is observed in the Mississippi River influenced areas. In addition to mixing control, biological processes such a calcification and benthic alkalinity production may also affect ocean margin alkalinity distribution. Therefore, deriving inorganic carbon system information in coastal oceans using alkalinity-salinity relationships, in particular, those of generic nature, may lead to significant errors.
Aragonite saturation states in estuaries along a climate gradient in the northwestern Gulf of Mexico
(Frontiers in Environmental Science, 2022-10-10) Hu, Xinping; Yao, Hongming; McCutcheon, Melissa; Dias, Larissa; Staryk, Cory; Wetz, Michael; Montagna, Paul
In the northwestern Gulf of Mexico (nwGOM), the coastal climate shifts abruptly from the humid northeast to the semiarid southwest within a narrow latitudinal range. The climate effect plays an important role in controlling freshwater discharge into the shallow estuaries in this region. In addition to diminishing freshwater runoff down the coast, evaporation also increases substantially. Hence, these estuaries show increasing salinity along the coastline due to the large difference in freshwater inflow balance (river runoff and precipitation minus evaporation and diversion). However, this spatial gradient can be disrupted by intense storm events as a copious amount of precipitation leads to river flooding, which can cause temporary freshening of these systems in extreme cases, in addition to freshwater-induced ephemeral stratification. We examined estuarine water aragonite saturation state (Ωarag) data collected between 2014 and 2018, covering a period of contrasting hydrological conditions, from the initial drought to multiple flooding events, including a brief period that was influenced by a category 4 hurricane. Based on freshwater availability, these estuaries exhibited a diminishing Ωarag fluctuation from the most freshwater enriched Guadalupe Estuary to the most freshwaterstarved Nueces Estuary. While Ωarag values were usually much higher than the threshold level (Ωarag = 1), brief freshwater discharge events and subsequent low oxygen levels in the lower water column led to episodic corrosive conditions. Based on previously obtained Ωarag temporal trends and Ωarag values obtained in this study, we estimated the time of emergence (ToE) for Ωarag. Not only did estuaries show decreasing ToE with diminishing freshwater availability but the sub-embayments of individual estuaries that had a less freshwater influence also had shorter ToE. This spatial pattern suggests that planning coastal restoration efforts, especially for shellfish organisms, should emphasize areas with longer ToE.
An assessment of ocean margin anaerobic processes on oceanic alkalinity budget
(Global Biogeochem, 2011-07-08) Hu, Xinping; Cai, Wei-Jun
Recent interest in the ocean’s capacity to absorb atmospheric CO2 and buffer the accompanying “ocean acidification” has prompted discussions on the magnitude of ocean margin alkalinity production via anaerobic processes. However, available estimates are largely based on gross reaction rates or misconceptions regarding reaction stoichiometry. In this paper, we argue that net alkalinity gain does not result from the internal cycling of nitrogen and sulfur species or from the reduction of metal oxides. Instead, only the processes that involve permanent loss of anaerobic remineralization products, i.e., nitrogen gas from net denitrification and reduced sulfur (i.e., pyrite burial) from net sulfate reduction, could contribute to this anaerobic alkalinity production. Our revised estimate of net alkalinity production from anaerobic processes is on the order of 4–5 Tmol yr−1 in global ocean margins that include both continental shelves and oxygen minimum zones, significantly smaller than the previously estimated rate of 16–31 Tmol yr−1 . In addition, pyrite burial in coastal habitats (salt marshes, mangroves, and seagrass meadows) may contribute another 0.1–1.1 Tmol yr−1 , although their long‐term effect is not yet clear under current changing climate conditions and rising sea levels. Finally, we propose that these alkalinity production reactions can be viewed as “charge transfer” processes, in which negative charges of nitrate and sulfate ions are converted to those of bicarbonate along with a net loss of these oxidative anions.
Best Practice Data Standards for Discrete Chemical Oceanographic Observations
(Frontiers in Marine Science, 2022-01-21) Jiang, Li-Qing; Pierrot, Denis; Wanninkhof, Rik; Feely, Richard A.; Tilbrook, Bronte; Alin, Simone; Barbero, Leticia; Byrne, Robert H.; Carter, Brendan R.; Dickson, Andrew G.; Gattuso, Jean-Pierre; Greeley, Dana; Hoppema, Mario; Humphreys, Matthew P.; Karstensen, Johannes; Lange, Nico; Lauvset, Siv K.; Lewis, Ernie R.; Olsen, Are; Pérez, Fiz F.; Sabine, Christopher; Sharp, Jonathan D.; Tanhua, Toste; Trull, Thomas W.; Velo, Anton; Allegra, Andrew J.; Barker, Paul; Burger, Eugene; Cai, Wei-Jun; Chen, Chen-Tung A.; Cross, Jessica; Garcia, Hernan; Hernandez-Ayon, Jose Martin; Hu, Xinping; Kozyr, Alex; Langdon, Chris; Lee, Kitack; Salisbury, Joe; Wang, Zhaohui Aleck; Xue, Liang
Effective data management plays a key role in oceanographic research as cruise-based data, collected from different laboratories and expeditions, are commonly compiled to investigate regional to global oceanographic processes. Here we describe new and updated best practice data standards for discrete chemical oceanographic observations, specifically those dealing with column header abbreviations, quality control flags, missing value indicators, and standardized calculation of certain properties. These data standards have been developed with the goals of improving the current practices of the scientific community and promoting their international usage. These guidelines are intended to standardize data files for data sharing and submission into permanent archives. They will facilitate future quality control and synthesis efforts and lead to better data interpretation. In turn, this will promote research in ocean biogeochemistry, such as studies of carbon cycling and ocean acidification, on regional to global scales. These best practice standards are not mandatory. Agencies, institutes, universities, or research vessels can continue using different data standards if it is important for them to maintain historical consistency. However, it is hoped that they will be adopted as widely as possible to facilitate consistency and to achieve the goals stated above.
A biogeochemical alkalinity sink in a shallow, semiarid estuary of the Northwestern Gulf of Mexico
(Aquatic Geochemistry, 2022-12-08) Dias, Larissa; Hu, Xinping; Yin, Hang
Estuarine total alkalinity (TA), which buffers against acidification, is temporally and spatially variable and regulated by complex, interacting hydrologic and biogeochemical processes. During periods of net evaporation (drought), the Mission-Aransas Estuary (MAE) of the northwestern Gulf of Mexico experienced TA losses beyond what can be attributed to calcification. The contribution of sedimentary oxidation of reduced sulfur to the TA loss was examined in this study. Water column samples were collected from five stations within MAE and analyzed for salinity, TA, and calcium ion concentrations. Sediment samples from four of these monitoring stations and one additional station within MAE were collected and incubated between 2018 and 2021. TA, calcium, magnesium, and sulfate ion concentrations were analyzed for these incubations. Production of sulfate along with TA consumption (or production) beyond what can be attributed to calcification (or carbonate dissolution) was observed. These results suggest that oxidation of reduced sulfur consumed TA in MAE during droughts. We estimate that the upper limit of TA consumption due to reduced sulfur oxidation can be as much as 4.60 × 108 mol day−1 in MAE. This biogeochemical TA sink may be present in other similar subtropical, freshwater-starved estuaries around the world.
Carbon cycling in the North American coastal ocean: a synthesis
(2019-03-27) Fennel, Katja; Alin, Simone; Barbero, Leticia; Evans, Wiley; Bourgeois, Timothée; Cooley, Sarah; Dunne, John; Feely, Richard A.; Hernandez-Ayon, Jose Martin; Hu, Xinping; Lohrenz, Steven; Muller-Karger, Frank; Najjar, Raymond; Robbins, Lisa; Shadwick, Elizabeth; Siedlecki, Samantha; Steiner, Nadja; Sutton, Adrienne; Turk, Daniela; Vlahos, Penny; Wang, Zhaohui Aleck
A quantification of carbon fluxes in the coastal ocean and across its boundaries with the atmosphere, land, and the open ocean is important for assessing the current state and projecting future trends in ocean carbon uptake and coastal ocean acidification, but this is currently a missing component of global carbon budgeting. This synthesis reviews recent progress in characterizing these carbon fluxes for the North American coastal ocean. Several observing networks and high-resolution regional models are now available. Recent efforts have focused primarily on quantifying the net air–sea exchange of carbon dioxide (CO2). Some studies have estimated other key fluxes, such as the exchange of organic and inorganic carbon between shelves and the open ocean. Available estimates of air–sea CO2 flux, informed by more than a decade of observations, indicate that the North American Exclusive Economic Zone (EEZ) acts as a sink of 160±80 Tg C yr−1, although this flux is not well constrained. The Arctic and sub-Arctic, mid-latitude Atlantic, and mid-latitude Pacific portions of the EEZ account for 104, 62, and −3.7 Tg C yr−1, respectively, while making up 51 %, 25 %, and 24 % of the total area, respectively. Combining the net uptake of 160±80 Tg C yr−1 with an estimated carbon input from land of 106±30 Tg C yr−1 minus an estimated burial of 65±55 Tg C yr−1 and an estimated accumulation of dissolved carbon in EEZ waters of 50±25 Tg C yr−1 implies a carbon export of 151±105 Tg C yr−1 to the open ocean. The increasing concentration of inorganic carbon in coastal and open-ocean waters leads to ocean acidification. As a result, conditions favoring the dissolution of calcium carbonate occur regularly in subsurface coastal waters in the Arctic, which are naturally prone to low pH, and the North Pacific, where upwelling of deep, carbon-rich waters has intensified. Expanded monitoring and extension of existing model capabilities are required to provide more reliable coastal carbon budgets, projections of future states of the coastal ocean, and quantification of anthropogenic carbon contributions.
Continental shelves as a variable but increasing global sink for atmospheric carbon dioxide
(2018-01-31) Laruelle, Goulven G.; Cai, Wei-Jun; Hu, Xinping; Gruber, Nicolas; Mackenzie, Fred T.; Regnier, Pierre
It has been speculated that the partial pressure of carbon dioxide (pCO2) in shelf waters may lag the rise in atmospheric CO2. Here, we show that this is the case across many shelf regions, implying a tendency for enhanced shelf uptake of atmospheric CO2. This result is based on analysis of long-term trends in the air–sea pCO2 gradient (ΔpCO2) using a global surface ocean pCO2 database spanning a period of up to 35 years. Using wintertime data only, we find that ΔpCO2 increased in 653 of the 825 0.5° cells for which a trend could be calculated, with 325 of these cells showing a significant increase in excess of +0.5 μatm yr−1 (p < 0.05). Although noisier, the deseasonalized annual data suggest similar results. If this were a global trend, it would support the idea that shelves might have switched from a source to a sink of CO2 during the last century.
Coral disease outbreak at the remote Flower Garden Banks, Gulf of Mexico
(Frontiers in Marine Science, 2023-01-26) Johnston, Michelle; Studivan, Michael; Enochs, Ian; Correa, Adrienne; Besemer, Nicole; Eckert, Ryan; Edwards, Kimberly; Hannum, Ryan; Hu, Xinping; Nuttall, Marissa; O'Connell, Kelley; Palacio-Castro, Ana; Schmahl, George; Sturm, Alexis; Ushijima, Blake; Voss, Joshua
East and West Flower Garden Bank (FGB) are part of Flower Garden Banks National Marine Sanctuary (FGBNMS) in the northwest Gulf of Mexico. This geographically-isolated reef system contains extensive coral communities with the highest coral cover (>50%) in the continental United States due, in part, to their remoteness and depth, and have historically exhibited low incidence of coral disease and bleaching despite ocean warming. Yet in late August 2022, disease-like lesions on seven coral species were reported during routine monitoring surveys on East and West FGB (2.1–2.6% prevalence). A series of rapid response cruises were conducted in September and October 2022 focused on 1) characterizing signs and epidemiological aspects of the disease across FGB and within long-term monitoring sites, 2) treating affected coral colonies with Base 2B plus amoxicillin, and 3) collecting baseline images through photostations and photomosaics. Marginal and/or multi-focal lesions and tissue loss were observed, often associated with substantial fish and invertebrate predation, affecting the dominant coral species Pseudodiploria strigosa (7–8% lesion prevalence), Colpophyllia natans (11–18%), and Orbicella spp. (1%). Characterizing this disease event during its early epidemic phase at East and West FGB provides a critical opportunity to observe how coral disease functions in a relatively healthy coral ecosystem versus on reefs chronically affected by various stressors (e.g., Caribbean reefs adjacent to urban centers). Insights into the etiology, spread, and impacts of the disease can ultimately inform efforts to mitigate its effects on coral communities.
Coral Energy Reserves and Calcification in a High-CO2 World at Two Temperatures
(2013-10-11) Schoepf, Verena; Grottoli, Andréa G.; Warner, Mark E.; Cai, Wei-Jun; Melman, Todd F.; Hoadley, Kenneth D.; Pettay, D. Tye; Hu, Xinping; Li, Qian; Xu, Hui; Wang, Yongchen; Matsui, Yohei; Baumann, Justin H.
Rising atmospheric CO2 concentrations threaten coral reefs globally by causing ocean acidification (OA) and warming. Yet, the combined effects of elevated pCO2 and temperature on coral physiology and resilience remain poorly understood. While coral calcification and energy reserves are important health indicators, no studies to date have measured energy reserve pools (i.e., lipid, protein, and carbohydrate) together with calcification under OA conditions under different temperature scenarios. Four coral species, Acropora millepora, Montipora monasteriata, Pocillopora damicornis, Turbinaria reniformis, were reared under a total of six conditions for 3.5 weeks, representing three pCO2 levels (382, 607, 741 µatm), and two temperature regimes (26.5, 29.0°C) within each pCO2 level. After one month under experimental conditions, only A. millepora decreased calcification (−53%) in response to seawater pCO2 expected by the end of this century, whereas the other three species maintained calcification rates even when both pCO2 and temperature were elevated. Coral energy reserves showed mixed responses to elevated pCO2 and temperature, and were either unaffected or displayed nonlinear responses with both the lowest and highest concentrations often observed at the mid-pCO2 level of 607 µatm. Biweekly feeding may have helped corals maintain calcification rates and energy reserves under these conditions. Temperature often modulated the response of many aspects of coral physiology to OA, and both mitigated and worsened pCO2 effects. This demonstrates for the first time that coral energy reserves are generally not metabolized to sustain calcification under OA, which has important implications for coral health and bleaching resilience in a high-CO2 world. Overall, these findings suggest that some corals could be more resistant to simultaneously warming and acidifying oceans than previously expected.
Corrigendum: Disparate responses of carbonate system in two adjacent subtropical estuaries CV-5 to the influence of Hurricane Harvey - A case study
(Frontiers in Marine Science, 2021-01-25) Hu, Xinping; Yao, Hongming; Staryk, Cory J.; McCutcheon, Melissa R.; Wetz, Michael S.; Walker, Lily
Disparate responses of carbonate system in two adjacent subtropical estuaries to the influence of Hurricane Harvey - A case study
(Frontiers in Marine Science, 2020-01-31) Hu, Xinping; Yao, Hongming; Staryk, Cory J.; McCutcheon, Melissa R.; Wetz, Michael S.; Walker, Lily
Two adjacent estuaries in the northwestern Gulf of Mexico (GOM) (Mission–Aransas or MAE and Guadalupe–San Antonio or GE), despite their close proximity and similar extents of freshening caused by Hurricane Harvey, exhibited different behaviors in their post-hurricane carbonate chemistry and CO2 fluxes. The oligotrophic MAE had little change in post-Harvey CO2 partial pressure (pCO2) and CO2 flux even though the center of Harvey passed right through, while GE showed a large post-Harvey increases in both pCO2 and CO2 flux, which were accompanied by a brief period of low dissolved oxygen (DO) conditions likely due to the large input of organic matter mobilized by the hurricane. The differences in the carbonate chemistry and CO2 fluxes were attributed to the differences in the watersheds from which these estuaries receive freshwater. The GE watershed is larger and covers urbanized areas, and, as a result, GE is considered relatively eutrophic. On the other hand, the MAE watershed is smaller, much less populous, and MAE is oligotrophic when river discharge is low. Despite that Harvey passed through MAE, the induced changes in carbonate chemistry and CO2 flux there were less conspicuous than those in GE. This study suggested that disturbances by strong storms to estuarine carbon cycle may not be uniform even on such a small spatial scale. Therefore, disparate responses to these disturbances need to be studied on a case-by-case basis.
Effect of hydrological variability on the biogeochemistry of estuaries across a regional climatic gradient
(Association for the Sciences of Limnology and Oceanography, 2018-08-15) Montagna, Paul A.; Hu, Xinping; Palmer, Terence A.; Wetz, Michael S.
Given projected changes in river flow to coastal regions worldwide due to climate change and increasing human freshwater demands, it is necessary to determine the role hydrology plays in regulating the biogeochemistry of estuaries. A climatic gradient exists along the Texas coast where freshwater inflow balance ranges from hydrologically positive to negative (where evaporation exceeds inflow) within a narrow latitudinal band, providing a natural experiment for examining inflow effects. Four Texas estuaries ranging from mesosaline to hypersaline were studied for 3 yr to determine how hydrological changes alter the biogeochemistry within and among the estuaries. Trends in dissolved inorganic nutrients, chlorophyll, dissolved organic matter, and carbonate chemistry indicated that these estuaries had drastically different biogeochemical signatures. Nutrients and chlorophyll patterns illustrated an emerging paradigm where phytoplankton biomass in positive estuaries is supported by “new” nitrogen from riverine input, while high concentrations of reduced nitrogen (organic, ammonium) allowed for high chlorophyll in the negative estuary. For carbonate chemistry, a positive estuary receiving river input from a limestone-dominated watershed was well-buffered under moderate to high freshwater inflow conditions. When weathering products were diluted during high-flow conditions, there is carbonate undersaturation (for aragonite) and decreases in pH. However, “acidification” was not observed in the negative estuary because evaporation concentrated the dissolved species and increased buffering capacity. Hydrological changes over spatial gradients are analogous to climatic changes over time, meaning climate change forecasts of higher temperatures and decreased precipitation can make the biogeochemistry of fresher estuaries change to the patterns of saltier estuaries.
Effect of Organic Alkalinity on Seawater Buffer Capacity: A Numerical Exploration
(Springer Nature, 2020-04-20) Hu, Xinping
Organic alkalinity is a poorly understood component of total titration alkalinity in aquatic environments. Using a numerical method, the effects of organic acid (HOA) and its conjugate base (OA−) on seawater carbonate chemistry and buffer behaviors, as well as those in a hypothetical estuarine mixing zone, are explored under both closed- and open-system conditions. The simulation results show that HOA addition leads to pCO2 increase and pH decrease in a closed system when total dissolved inorganic carbon (DIC) remains the same. If opened to the atmosphere (pCO2=400 µatm), CO2 degassing and re-equilibration would cause depressed pH compared to the unperturbed seawater, but the seawater buffer to pH change [equation] indicates that weaker organic acid (i.e., higher pKa) results in higher bufer capacity (greater βDIC) than the unperturbed seawater. In comparison, OA− (with accompanying cations) in the form of net alkalinity addition leads to pCO2 decrease in a closed system. After re-equilibrating with the atmosphere, the resulting perturbed seawater has higher pH and βDIC than the unperturbed seawater. If river water has organic alkalinity, pH in the estuarine mixing zone is always lower than those caused by a mixing between organic alkalinity-free river (at constant total alkalinity) and ocean waters, regardless of the pKa values. On the other hand, organic alkalinity with higher pKa provides slightly greater βDIC in the mixing zone, and that with lower pKa either results in large CO2 oversaturation (closed system) or reduced βDIC (in mid to high salinity in the closed system or the entire mixing zone in the open system). Finally, despite the various effects on seawater buffer through either HOA or OA− addition, destruction of organic molecules including organic alkalinity via biogeochemical reactions should result in a net CO2 loss from seawater. Nevertheless, the significance of this organic alkalinity, especially that comes from organic acids that are not accounted for under the currently recognized “zero proton level” (Dickson in Deep Sea Res 28:609–623, 1981), remains unknown thus a potentially interesting and relevant research topic in studying oceanic alkalinity cycle.
Effects of climate change on metabolite accumulation in freshwater and marine cyanobacteria
(Elsevier Inc., 2021-09-02) Huang, I-Shuo; Hu, Xinping; Abdulla, Hussain; Zimba, Paul V.
Global climate change and anthropogenic nutrient inputs are responsible for increased frequency of cyanobacterial blooms that potentially contain 55 classes of bioactive metabolites. This study investigated the effects of CO2 availability and concomittant pH levels on two cyanobacteria that produce microcystins: a marine cf. Synechocystis sp. and a freshwater Microcystis aeruginosa. Cyanobacterial strains were semi-continuously cultured in mesotrophic growth media at pH 7.5, 7.8, 8.2, and 8.5 via a combination of CO2 addition and control of alkalinity. The cell concentration between treatments was not significantly different and nutrient availability was not limited. Concentration of most known cyanobacterial bioactive metabolites in both cyanobacterial strains increased as CO2 increased. At pH 7.8, bioactive metabolite intracellular concentration in M. aeruginosa and Synechocystis was 1.5 and 1.2 times greater than the other three treatments, respectively. Intracellular concentration of microginin in M. aeruginosa at pH 7.5 was reduced by 90% compared to the other three treatments. Intracellular concentration of microcyclamide-bistratamide B was lower in M. aeruginosa and higher in Synechocystis at elevated CO2 concentration. M. aeruginosa products were more diverse metabolites than Synechocystis. The diversity of accumulated metabolites in M. aeruginosa increased as CO2 increased, whereas the metabolite diversity in Synechocystis decreased as pH decreased. Overall, intracellular concentration of bioactive metabolites was higher at greater CO2 concentrations; marine and freshwater cyanobacteria had different allocation products when exposed to differing CO2 environments.
Integrating High-Resolution Coastal Acidification Monitoring Data Across Seven United States Estuaries
(Frontiers in Marine Science, 2021-08-19) Rosenau, Nicholas A.; Galavotti, Holly; Yates, Kimberly K.; Bohlen, Curtis C.; Hunt, Christopher W.; Liebman, Matthew; Brown, Cheryl A.; Pacella, Stephen R.; Largier, John L.; Nielsen, Karina J.; Hu, Xinping; McCutcheon, Melissa R.; Vasslides, James M.; Poach, Matthew; Ford, Tom; Johnston, Karina; Steele, Alex
Beginning in 2015, the United States Environmental Protection Agency’s (EPA’s) National Estuary Program (NEP) started a collaboration with partners in seven estuaries along the East Coast (Barnegat Bay; Casco Bay), West Coast (Santa Monica Bay; San Francisco Bay; Tillamook Bay), and the Gulf of Mexico (GOM) Coast (Tampa Bay; Mission-Aransas Estuary) of the United States to expand the use of autonomous monitoring of partial pressure of carbon dioxide (pCO2) and pH. Analysis of high-frequency (hourly to sub-hourly) coastal acidification data including pCO2, pH, temperature, salinity, and dissolved oxygen (DO) indicate that the sensors effectively captured key parameter measurements under challenging environmental conditions, allowing for an initial characterization of daily to seasonal trends in carbonate chemistry across a range of estuarine settings. Multi-year monitoring showed that across all water bodies temperature and pCO2 covaried, suggesting that pCO2 variability was governed, in part, by seasonal temperature changes with average pCO2 being lower in cooler, winter months and higher in warmer, summer months. Furthermore, the timing of seasonal shifts towards increasing (or decreasing) pCO2 varied by location and appears to be related to regional climate conditions. Specifically, pCO2 increases began earlier in the year in warmer water, lower latitude water bodies in the GOM (Tampa Bay; Mission-Aransas Estuary) as compared with cooler water, higher latitude water bodies in the northeast (Barnegat Bay; Casco Bay), and upwelling-influenced West Coast water bodies (Tillamook Bay; Santa Monica Bay; San Francisco Bay). Results suggest that both thermal and non-thermal influences are important drivers of pCO2 in Tampa Bay and Mission-Aransas Estuary. Conversely, non-thermal processes, most notably the biogeochemical structure of coastal upwelling, appear to be largely responsible for the observed pCO2 values in West Coast water bodies. The co-occurrence of high salinity, high pCO2, low DO, and low temperature water in Santa Monica Bay and San Francisco Bay characterize the coastal upwelling paradigm that is also evident in Tillamook Bay when upwelling dominates freshwater runoff and local processes. These data demonstrate that high-quality carbonate chemistry observations can be recorded from estuarine environments using autonomous sensors originally designed for open-ocean settings.
Interpreting biogeochemical processes through the relationship between total alkalinity and dissolved inorganic carbon: Theoretical basis and limitations
(Limnology and Oceanography Methods, 2024-03-14) Hang Yin; Xinping Hu
The marine carbonate system is influenced by anthropogenic CO2 uptake, biogeochemical processes, and physical changes that involve freshwater input and removal. Two frequently used parameters to quantify seawater carbonate system are total alkalinity (TA) and total dissolved inorganic carbon (DIC). To account for the physical changes, both TA and DIC are usually normalized to a reference salinity (i.e., nTA and nDIC), and then the relationship between nTA and nDIC is used to identify major biogeochemical processes that regulate the carbonate system, based on process-specific reaction stoichiometry. However, the theoretical basis of this interpretation has not been holistically examined. In this study, we validated this method under idealized conditions and discussed the associated assumptions and limitations. Furthermore, we applied this method to interpret field TA and DIC data from a lagoonal estuary in the northwestern Gulf of Mexico. Our results demonstrated that evaluating field data that encompass multiple stations and time periods could be problematic. In addition, various combinations of biogeochemical processes can lead to the same nTA–nDIC relationship, even though the relative importance of each individual process may vary significantly. Therefore, the stoichiometric relationship relying solely on TA and DIC data is not a definitive approach for uncovering dominant biogeochemical processes. Instead, measurements of process-specific parameters are necessary.
Long-Term Trends in Estuarine Carbonate Chemistry in the Northwestern Gulf of Mexico
(Frontiers in Marine Science, 2022-03-03) McCutcheon, Melissa R.; Hu, Xinping
A four-decade dataset that spans seven estuaries along a latitudinal gradient in the northwestern Gulf of Mexico and includes measurements of pH and total alkalinity was used to calculate partial pressure of CO2 (pCO2), dissolved inorganic carbon (DIC), saturation state of aragonite (ΩAr), and a buffer factor (βDIC, which measures the response of proton concentration or pH to DIC concentration change) and examine long-term trends and spatial patterns in these parameters. With the notable exception of the northernmost and southernmost estuaries (and selected stations near freshwater input), these estuaries have generally experienced long-term increases in pCO2 and decreases in DIC, ΩAr, and βDIC, with the magnitude of change generally increasing from north to south. At all stations with increasing pCO2, the rate of increase exceeded the rate of increase in atmospheric pCO2, indicating that these estuaries have become a greater source of CO2 to the atmosphere over the last few decades. The decreases in ΩAr have yet to cause ΩAr to near undersaturation, but even the observed decreases may have the potential to decrease calcification rates in important estuarine calcifiers like oysters. The decreases in βDIC directly indicate that these estuaries have experienced continually greater change in pH in the context of ocean acidification.
Microelectrode characterization of coral daytime interior pH and carbonate chemistry
(Nature Communications, 2016-04-04) Cai, Wei-Jun; Ma, Yuening; Hopkinson, Brian M.; Grottoli, Andrea G.; Warner, Mark E.; Ding, Qian; Hu, Xinping; Yuan, Xiangchen; Schoepf, Verena; Xu, Hui; Han, Chenhua; Melman, Todd F.; Hoadley, Kenneth D.; Pettay, D. Tye; Matsui, Yohei; Baumann, Justin H.; Levas, Stephen; Ying, Ye; Wang, Yongchen
Reliably predicting how coral calcification may respond to ocean acidification and warming depends on our understanding of coral calcification mechanisms. However, the concentration and speciation of dissolved inorganic carbon (DIC) inside corals remain unclear, as only pH has been measured while a necessary second parameter to constrain carbonate chemistry has been missing. Here we report the first carbonate ion concentration ([CO3 2 ]) measurements together with pH inside corals during the light period. We observe sharp increases in [CO3 2 ] and pH from the gastric cavity to the calcifying fluid, confirming the existence of a proton (H þ ) pumping mechanism. We also show that corals can achieve a high aragonite saturation state (Oarag) in the calcifying fluid by elevating pH while at the same time keeping [DIC] low. Such a mechanism may require less H þ -pumping and energy for upregulating pH compared with the high [DIC] scenario and thus may allow corals to be more resistant to climate change related stressors.
Microelectrode characterization of coral daytime interior pH and carbonate chemistry
(2016-04-04) Cai, Wei-Jun; Ma, Yuening; Hopkinson, Brian M.; Grottoli, Andréa G.; Warner, Mark E.; Ding, Qian; Hu, Xinping; Yuan, Xiangchen; Schoepf, Verena; Xu, Hui; Han, Chenhua; Melman, Todd F.; Hoadley, Kenneth D.; Pettay, D. Tye; Matsui, Yohei; Baumann, Justin H.; Levas, Stephen; Ying, Ye; Wang, Yongchen
Reliably predicting how coral calcification may respond to ocean acidification and warming depends on our understanding of coral calcification mechanisms. However, the concentration and speciation of dissolved inorganic carbon (DIC) inside corals remain unclear, as only pH has been measured while a necessary second parameter to constrain carbonate chemistry has been missing. Here we report the first carbonate ion concentration ([CO32−]) measurements together with pH inside corals during the light period. We observe sharp increases in [CO32−] and pH from the gastric cavity to the calcifying fluid, confirming the existence of a proton (H+) pumping mechanism. We also show that corals can achieve a high aragonite saturation state (Ωarag) in the calcifying fluid by elevating pH while at the same time keeping [DIC] low. Such a mechanism may require less H+-pumping and energy for upregulating pH compared with the high [DIC] scenario and thus may allow corals to be more resistant to climate change related stressors.
Ocean acidification in the Gulf of Mexico: Drivers, impacts, and unknowns
(Progress in Oceanography, 2022-10-04) Osborne, Emily; Hu, Xinping; Hall, Emily; Yates, Kimberly; Vreeland-Dawson, Jennifer; Shamberger, Katie; Barbero, Leticia; Hernandez-Ayon, J. Martin; Gomez, Fabian; Hicks, Tacey; Xu, Yuan-Yuan; McCutcheon, Melissa; Acquafredda, Michael; Chapa-Balcorta, Cecilia; Norzagaray, Orion; Pierrot, Denis; Munoz-Caravaca, Alain; Dobson, Kerri; Williams, Nancy; Rabalais, Nancy; Dash, Padmanava
Ocean acidification (OA) has resulted in global-scale changes in ocean chemistry, which can disturb marine organisms and ecosystems. Despite its extensively populated coastline, many marine-dependent communities, and valuable economies, the Gulf of Mexico (GOM) remains a relatively understudied region with respect to acidification. In general, the warm waters of the GOM are better buffered from acidification compared to higher latitude seas, yet long-term acidification has been documented in several GOM regions. OA within the GOM is recognized as spatially variable, particularly within the coastal zone where numerous physical and biogeochemical processes contribute to carbonate chemistry dynamics. The historical progression of OA within the entire GOM is difficult to assess because only a few dedicated long-term monitoring sites have recently been established, and full-water column observations are limited. However, environmental drivers on smaller scales that affect GOM acidification were found to include freshwater, nutrient, and carbonate discharge from large rivers; ocean warming, circulation and residence times; and episodic extreme weather events. GOM marine ecosystems provide essential services, including coastline protection and carbon dioxide removal, and habitats for many marine species that are economically and ecologically important. However, organismal and ecosystem responses to OA are not well constrained for the GOM due to a lack of studies examining the specific effects of OA on regionally relevant species under contemporary and projected conditions. Tackling the vast number of remaining scientific unknowns in this region can be coordinated through regional capacity networks, such as the Gulf of Mexico Coastal Acidification Network (GCAN), working to achieve a system-wide understanding of Gulf OA and its impacts. Here we synthesize the current peer-reviewed literature on GOM acidification across the ocean-estuarine continuum and identify critical knowledge, research, and monitoring gaps that limit our current understanding of environmental, ecological, and socioeconomic impacts from acidification.

Browse

Browsing Ecosystem Science & Modeling by Title