For over two decades, NOAA’s Pacific Marine Environmental Laboratory (PMEL) has been developing and deploying autonomous ocean carbon measurement technologies. PMEL currently maintains a network of ...air-sea CO₂ and ocean acidification time-series measurements on 33 surface buoys, including the world’s longest record of air-sea CO₂ measured from a buoy. These sites are located in every ocean basin and in a variety of ecosystems, from coastal to open ocean and subpolar to tropical. The network provides more than half of today’s ocean carbonate chemistry timeseries records that qualify as long-term, publicly available, and collected at subseasonal timescales. Here, we briefly review the motivation for establishing the network, the research and applications made possible from the observations, and how sustained autonomous time series generate unique information about a changing ocean needed to inform mitigation and adaptation approaches in a changing world.
Abstract
The subpolar Southern Ocean is a critical region where CO
2
outgassing influences the global mean air-sea CO
2
flux (F
CO2
). However, the processes controlling the outgassing remain ...elusive. We show, using a multi-glider dataset combining F
CO2
and ocean turbulence, that the air-sea gradient of CO
2
(∆pCO
2
) is modulated by synoptic storm-driven ocean variability (20 µatm, 1–10 days) through two processes. Ekman transport explains 60% of the variability, and entrainment drives strong episodic CO
2
outgassing events of 2–4 mol m
−2
yr
−1
. Extrapolation across the subpolar Southern Ocean using a process model shows how ocean fronts spatially modulate synoptic variability in ∆pCO
2
(6 µatm
2
average) and how spatial variations in stratification influence synoptic entrainment of deeper carbon into the mixed layer (3.5 mol m
−2
yr
−1
average). These results not only constrain aliased-driven uncertainties in F
CO2
but also the effects of synoptic variability on slower seasonal or longer ocean physics-carbon dynamics.
Seven years of data from the NOAA Kuroshio Extension Observatory (KEO) surface mooring, located in the North Pacific Ocean carbon sink region, were used to evaluate drivers of mixed‐layer carbon ...cycling. A time‐dependent mass balance approach relying on two carbon tracers was used to diagnostically evaluate how surface ocean processes influence mixed‐layer carbon concentrations over the annual cycle. Results indicate that the annual physical carbon input is predominantly balanced by biological carbon uptake during the intense spring bloom. Net annual gas exchange that adds carbon to the mixed layer and the opposing influence of net precipitation that dilutes carbon concentrations make up smaller contributions to the annual mixed‐layer carbon budget. Decomposing the biological term into annual net community production (aNCP) and calcium carbonate production (aCaCO3) yields 7 ± 3 mol C m−2 yr−1 aNCP and 0.5 ± 0.3 mol C m−2 yr−1 aCaCO3, giving an annually integrated particulate inorganic carbon to particulate organic carbon production ratio of 0.07 ± 0.05, as a lower limit. Although we find that vertical physical processes dominate carbon input to the mixed layer at KEO, it remains unclear how horizontal features, such as eddies, influence carbon production and export by altering nutrient supply as well as the depth of winter ventilation. Further research evaluating linkages between Kuroshio Extension jet instabilities, eddy activity, and nutrient supply mechanisms is needed to adequately characterize the drivers and sensitivities of carbon cycling near KEO.
Key Points
Annual net community production and calcium carbonate production in the mixed layer is 7 ± 3 and 0.5 ± 0.3 mol C m−2 yr−1, respectively
KEO exhibits an intense spring bloom period with an annual mean PIC:POC production ratio of 0.07 ± 0.05
Research linking nutrient supply mechanisms and Kuroshio Extension jet stability to annual carbon export is needed
The equatorial Pacific is the largest oceanic source of carbon dioxide to the atmosphere. This outgassing varies depending on the El Niño‐Southern Oscillation (ENSO) and decadal climate variability. ...New production, the amount of phytoplankton net primary production driven by upwelled nitrate, plays a significant role in modulating air‐sea CO2 fluxes as the biological carbon pump removes carbon from the surface ocean. We aim to understand how the physical drivers of sea surface temperature and wind speed influence interannual and decadal variability of the equatorial Pacific carbon cycle. In the equatorial Pacific, there are three biogeochemical regimes: the upwelling cold tongue east of 140°W and south of the equator (3°N–15°S); the eastern Pacific warm pool north of the equator (3°–15°N); and the 28.5°C western Pacific warm pool, west of 140°W. We find that between 2000 and 2020, air‐sea CO2 flux and ΔpCO2 increased in the cold tongue (45 mmolC m−2 yr−2, 1.5 μatm yr−1, respectively) but decreased elsewhere, while new production decreased everywhere. The western Pacific occasionally became a weak carbon sink, depending on ENSO and this sink was strongest at 165°E during central Pacific “Modoki” El Niño events. We find that changes in wind speed, temperature and ENSO frequency have altered the surface carbon budget. The mean basin‐wide (150°E−90°W and 15°N–15°S) new production for 2000–2020 was 1.2 ± 0.1 PgC yr−1 and air‐sea CO2 flux was 0.5 ± 0.1 PgC yr−1. New production decreased at −7.7 ± 1.6 TgC yr−2, compared to the CO2 flux trend of −1.7 ± 1.4 TgC yr−2.
Plain Language Summary
The equatorial Pacific is the largest source of carbon dioxide that outgasses from the ocean into the atmosphere. This outgassing varies depending on the El Niño‐Southern Oscillation (ENSO) and decadal changes in the climate. Winds in the eastern Pacific drive upwelling which supplies nutrients and carbon to the surface. Some of this carbon is outgassed to the atmosphere, some is consumed by phytoplankton and can either move through the food web or sink into the ocean interior. We are interested in how much carbon is removed from the surface equatorial Pacific through outgassing of carbon and biological consumption. We find that changes in wind speeds, surface temperatures, freshening surface water and changing patterns of ENSO have influenced the equatorial Pacific carbon budget. For example, between 2000 and 2020, CO2 release to the atmosphere increased in the upwelling zone but decreased elsewhere, while biological consumption decreased everywhere. The western Pacific occasionally absorbs carbon from the atmosphere during central Pacific “Modoki” El Niño events, a particular type of El Niño that is becoming more frequent.
Key Points
Decadal shifts in upwelling have increased CO2 flux in the cold tongue but not biological production, which is likely nutrient limited
Increasing frequency of central Pacific El Niño events may amplify decadal CO2 flux trends and drive sink conditions in the west
Increasing surface temperatures contribute to stratification and decreasing new production despite increasing dissolved inorganic carbon
Syntheses of carbonate chemistry spatial patterns are important for predicting ocean acidification impacts, but are lacking in coastal oceans. Here, we show that along the North American Atlantic and ...Gulf coasts the meridional distributions of dissolved inorganic carbon (DIC) and carbonate mineral saturation state (Ω) are controlled by partial equilibrium with the atmosphere resulting in relatively low DIC and high Ω in warm southern waters and the opposite in cold northern waters. However, pH and the partial pressure of CO
(pCO
) do not exhibit a simple spatial pattern and are controlled by local physical and net biological processes which impede equilibrium with the atmosphere. Along the Pacific coast, upwelling brings subsurface waters with low Ω and pH to the surface where net biological production works to raise their values. Different temperature sensitivities of carbonate properties and different timescales of influencing processes lead to contrasting property distributions within and among margins.
The equatorial Pacific is a dynamic region that plays an important role in the global carbon cycle. This region is the largest oceanic source of carbon dioxide (CO2) to the atmosphere, which varies ...interannually dependent on the El Niño‐Southern Oscillation (ENSO) and other climatic and oceanic drivers. We present high‐resolution observations of surface ocean CO2 partial pressure (pCO2) at four fixed locations in the Niño 3.4 area with data sets encompassing 10 ENSO warm and cold events from 1997 to 2011. The mooring observations confirm that ENSO controls much of the interannual variability in surface seawater pCO2 with values ranging from 315 to 578 µatm. The mooring time series also capture the temporal variability necessary to make the first estimates of long‐term pH trends in the equatorial Pacific, which suggests that the combination of ocean acidification and decadal variability creates conditions for high rates of pH change since the beginning of the mooring record. Anthropogenic CO2 increases play a dominant role in significant observed seawater pCO2 trends of +2.3 to +3.3 µatm yr−1 and pH trends of −0.0018 to −0.0026 yr−1 across the full time series in this region. However, increased upwelling driven by increased trade winds, a shallower thermocline, and increased frequency of La Niña events also contribute an average of 40% of the observed trends since 1998. These trends are higher than previous estimates based on underway observations and suggest that the equatorial Pacific is contributing a greater amount of CO2 to the atmospheric CO2 inventory over the last decade.
Key Points
Equatorial Pacific pCO2 trends are higher than global atmospheric trends
High pCO2 and pH trends are due to anthropogenic CO2 and increased upwelling
Increased CO2 outgassing since 1998 may be impacting atmospheric CO2
•The first full annual record of CO2 by MAPCO2 in the South Atlantic Bight.•Time series CO2 controls were quantitatively identified using a 1-D model.•River-influenced coastal system was vulnerable ...to terrestrial inputs.•River inputs can induce CO2 interannual variability.•Temporal under-sampling can greatly bias estimates of air–sea CO2 flux and NCP.
Carbon dioxide partial pressure (pCO2) in surface seawater was continuously recorded every three hours from 18 July 2006 through 31 October 2007 using a moored autonomous pCO2 (MAPCO2) system deployed on the Gray’s Reef buoy off the coast of Georgia, USA. Surface water pCO2 (average 373±52μatm) showed a clear seasonal pattern, undersaturated with respect to the atmosphere in cold months and generally oversaturated in warm months. High temporal resolution observations revealed important events not captured in previous ship-based observations, such as sporadically occurring biological CO2 uptake during April–June 2007. In addition to a qualitative analysis of the primary drivers of pCO2 variability based on property regressions, we quantified contributions of temperature, air–sea exchange, mixing, and biological processes to monthly pCO2 variations using a 1-D mass budget model. Although temperature played a dominant role in the annual cycle of pCO2, river inputs especially in the wet season, biological respiration in peak summer, and biological production during April–June 2007 also substantially influenced seawater pCO2. Furthermore, sea surface pCO2 was higher in September–October 2007 than in September–October 2006, associated with increased river inputs in fall 2007. On an annual basis this site was a moderate atmospheric CO2 sink, and was autotrophic as revealed by monthly mean net community production (NCP) in the mixed layer. If the sporadic short productive events during April–May 2007 were missed by the sampling schedule, one would conclude erroneously that the site is heterotrophic. While previous ship-based pCO2 data collected around this buoy site agreed with the buoy CO2 data on seasonal scales, high resolution buoy observations revealed that the cruise-based surveys undersampled temporal variability in coastal waters, which could greatly bias the estimates of air–sea CO2 fluxes or annual NCP, and even produce contradictory results.
The Blob was the early manifestation of the Northeast Pacific marine heat wave from 2013 to 2016. While the upper ocean temperature in the Blob has been well described, the impacts on marine ...biogeochemistry have not been fully studied. Here, we characterize and develop understanding of Eastern North Pacific upper ocean biogeochemical properties during the Winter of 2013–2014 using in situ observations, an observation‐based product, and reconstructions from a collection of ocean models. We find that the Blob is associated with significant upper ocean biogeochemical anomalies: A 5% increase in aragonite saturation state (temporary reprieve of ocean acidification) and a 3% decrease in oxygen concentration (enhanced deoxygenation). Anomalous advection and mixing drive the aragonite saturation anomaly, while anomalous heating and air‐sea gas exchange drive the oxygen anomaly. Marine heatwaves do not necessarily serve as an analog for future change as they may enhance or mitigate long‐term trends.
Plain Language Summary
The global ocean is experiencing major changes due to human‐made carbon emissions and climate change, leading to a warming ocean with increasing acidity and declining oxygen. On top of these long‐term changes in the ocean are short‐term extreme events, such as marine heatwaves. These extreme events quickly change the ocean state and can stress marine ecosystems in multiple ways. The Northeast Pacific marine heat wave (2013–2016) was one such marine heatwave. Here we focus on the early portion of this marine heatwave, called the Blob. While the ocean temperature changes during the event are well understood, the effects on ocean biogeochemistry have not been fully examined. In this study, we use an earth system model that accurately simulates the Blob to examine short‐term changes in oxygen and acidity. We find that the warming signal leads to a decline in the effects of ocean acidification, mainly due to changes in the movement of carbon, and lowers the amount of oxygen, due primarily to temperature‐driven effects. These results suggest that some effects of climate change may be exacerbated (warming) or mitigated (ocean acidification) by marine heatwaves.
Key Points
The North Pacific Blob had a distinct biogeochemical signature that is captured by observations and multiple ocean models
The Blob was characterized by anomalously high aragonite saturation states and anomalously low oxygen concentrations
The biogeochemical signature of the Blob was driven by changes in temperature and physical ocean circulation processes
Evidence of ocean acidification (OA) throughout the global ocean has galvanized some coastal communities to evaluate carbonate chemistry variations closer to home. An impediment to doing this ...effectively is that, often, only one carbonate system parameter is measured at a time, while two are required to fully constrain the inorganic carbon chemistry of seawater. In order to leverage the abundant singlecaibonate-parameter datasets in Washington State for more rigorous OA research, we have characterized an empirical relationship between total alkalinity (TA) and salinity (TA = 47.7 × S + 647; lσ = ±17 μmol kg⁻¹) for regional surface waters (≤25 m) that is robust in the salinity range from 20 to 35 for all seasons. The relationship was evaluated using 5 years of 3-h contemporaneous observations of salinity, carbon dioxide partial pressure (pCO₂), and pH from a surface mooring on the outer coast of Washington. In situ pCO₂ observations and salinity-based estimates of TA were used to calculate pH for comparison with in situ pH measurements. On average, the calculated pH values were 0.02 units lower than the measured pH values across multiple pH sensor deployments and showed extremely high fidelity in tracking the measured high-frequency pH variations. Our results indicate that the TA-salinity relationship will be a useful tool for expanding single-carbonate-parameter datasets in Washington State and quality controlling dual pCO₂-pH time senes.
A budget approach is used to disentangle drivers of the seasonal mixed layer carbon cycle at Station ALOHA (A Long‐term Oligotrophic Habitat Assessment) in the North Pacific Subtropical Gyre (NPSG). ...The budget utilizes data from the WHOTS (Woods Hole—Hawaii Ocean Time‐series Site) mooring, and the ship‐based Hawai'i Ocean Time‐series (HOT) in the NPSG, a region of significant oceanic carbon uptake. Parsing the carbon variations into process components allows an assessment of both the proportional contributions of mixed layer carbon drivers and the seasonal interplay of drawdown and supply from different processes. Annual net community production reported here is at the lower end of previously published data, while net community calcification estimates are 4‐ to 7‐fold higher than available sediment trap data, the only other estimate of calcium carbonate export at this location. Although the observed seasonal cycle in dissolved inorganic carbon in the NPSG has a relatively small amplitude, larger fluxes offset each other over an average year. Major supply comes from physical transport, especially lateral eddy transport throughout the year and entrainment in the winter, offset by biological carbon uptake in the spring. Gas exchange plays a smaller role, supplying carbon to the surface ocean between Dec‐May and outgassing in Jul‐Oct. Evaporation‐precipitation (E‐P) is variable with precipitation prevailing in the first half and evaporation in the second half of the year. The observed total alkalinity signal is largely governed by E‐P with a somewhat stronger net calcification signal in the wintertime.
Plain Language Summary
The ocean carbon cycle is a complicated system where chemical compounds react, are moved by ocean physics, altered by organisms, and exchange with CO2 in the atmosphere. To explore how the ocean will continue to take up CO2 from the atmosphere and how much will be removed into the deep ocean, we need to know how these processes influence ocean carbon. Here, we investigate them over a year. We create a model from observations of two carbon compounds, together with calculated estimates of processes (evaporation and precipitation, transport through the water, and air‐sea exchange) to back out the influence of two important reaction pairs executed by organisms: Photosynthesis and respiration, and calcification and dissolution. Over a year, the surface community at this location near Hawai'i in the Pacific photosynthesizes more than it respires, removing 53 g of CO2 per square meter. Also, marine calcifiers perform calcification, and our estimates are much higher than previous measurements from sediment traps. Gas exchange and evaporation‐precipitation vary with the seasons in opposite directions, and there are carbon inputs from horizontal transport throughout the year and from water column mixing in the winter.
Key Points
First calculation of community calcification with a budget approach at this location, results exceed reported sediment trap data
Independently constrained horizontal and vertical transport of dissolved inorganic carbon/total alkalinity. Largest annual supply: lateral inputs with strong eddy contribution
It is important to better characterize the physical, especially horizontal, transport of carbon to further investigate mixed layer carbon cycling
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