DeGrandpre
Michael D.
DeGrandpre
Michael D.
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ArticleSea surface pCO2 and O2 dynamics in the partially ice-covered Arctic Ocean(John Wiley & Sons, 2017-02-25) Islam, Fakhrul ; DeGrandpre, Michael D. ; Beatty, Cory ; Timmermans, Mary-Louise ; Krishfield, Richard A. ; Toole, John M. ; Laney, Samuel R.Understanding the physical and biogeochemical processes that control CO2 and dissolved oxygen (DO) dynamics in the Arctic Ocean (AO) is crucial for predicting future air-sea CO2 fluxes and ocean acidification. Past studies have primarily been conducted on the AO continental shelves during low-ice periods and we lack information on gas dynamics in the deep AO basins where ice typically inhibits contact with the atmosphere. To study these gas dynamics, in situ time-series data have been collected in the Canada Basin during late summer to autumn of 2012. Partial pressure of CO2 (pCO2), DO concentration, temperature, salinity, and chlorophyll-a fluorescence (Chl-a) were measured in the upper ocean in a range of sea ice states by two drifting instrument systems. Although the two systems were on average only 222 km apart, they experienced considerably different ice cover and external forcings during the 40–50 day periods when data were collected. The pCO2 levels at both locations were well below atmospheric saturation whereas DO was almost always slightly supersaturated. Modeling results suggest that air-sea gas exchange, net community production (NCP), and horizontal gradients were the main sources of pCO2 and DO variability in the sparsely ice-covered AO. In areas more densely covered by sea ice, horizontal gradients were the dominant source of variability, with no significant NCP in the surface mixed layer. If the AO reaches equilibrium with atmospheric CO2 as ice cover continues to decrease, aragonite saturation will drop from a present mean of 1.00 ± 0.02 to 0.86 ± 0.01.
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ArticleChanges in the arctic ocean carbon cycle with diminishing ice cover(American Geophysical Union, 2020-05-24) DeGrandpre, Michael D. ; Evans, Wiley ; Timmermans, Mary-Louise ; Krishfield, Richard A. ; Williams, William J. ; Steele, MichaelLess than three decades ago only a small fraction of the Arctic Ocean (AO) was ice free and then only for short periods. The ice cover kept sea surface pCO2 at levels lower relative to other ocean basins that have been exposed year round to ever increasing atmospheric levels. In this study, we evaluate sea surface pCO2 measurements collected over a 6‐year period along a fixed cruise track in the Canada Basin. The measurements show that mean pCO2 levels are significantly higher during low ice years. The pCO2 increase is likely driven by ocean surface heating and uptake of atmospheric CO2 with large interannual variability in the contributions of these processes. These findings suggest that increased ice‐free periods will further increase sea surface pCO2, reducing the Canada Basin's current role as a net sink of atmospheric CO2.
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ArticleAir-sea CO2 exchange in the equatorial Pacific(American Geophysical Union, 2004-08-28) McGillis, Wade R. ; Edson, James B. ; Zappa, Christopher J. ; Ware, Jonathan D. ; McKenna, Sean P. ; Terray, Eugene A. ; Hare, Jeffrey E. ; Fairall, Christopher W. ; Drennan, William M. ; Donelan, Mark A. ; DeGrandpre, Michael D. ; Wanninkhof, Rik ; Feely, Richard A.GasEx-2001, a 15-day air-sea carbon dioxide (CO2) exchange study conducted in the equatorial Pacific, used a combination of ships, buoys, and drifters equipped with ocean and atmospheric sensors to assess variability and surface mechanisms controlling air-sea CO2 fluxes. Direct covariance and profile method air-sea CO2 fluxes were measured together with the surface ocean and marine boundary layer processes. The study took place in February 2001 near 125°W, 3°S in a region of high CO2. The diurnal variation in the air-sea CO2 difference was 2.5%, driven predominantly by temperature effects on surface solubility. The wind speed was 6.0 ± 1.3 m s−1, and the atmospheric boundary layer was unstable with conditions over the range −1 < z/L < 0. Diurnal heat fluxes generated daytime surface ocean stratification and subsequent large nighttime buoyancy fluxes. The average CO2 flux from the ocean to the atmosphere was determined to be 3.9 mol m−2 yr−1, with nighttime CO2 fluxes increasing by 40% over daytime values because of a strong nighttime increase in (vertical) convective velocities. The 15 days of air-sea flux measurements taken during GasEx-2001 demonstrate some of the systematic environmental trends of the eastern equatorial Pacific Ocean. The fact that other physical processes, in addition to wind, were observed to control the rate of CO2 transfer from the ocean to the atmosphere indicates that these processes need to be taken into account in local and global biogeochemical models. These local processes can vary on regional and global scales. The GasEx-2001 results show a weak wind dependence but a strong variability in processes governed by the diurnal heating cycle. This implies that any changes in the incident radiation, including atmospheric cloud dynamics, phytoplankton biomass, and surface ocean stratification may have significant feedbacks on the amount and variability of air-sea gas exchange. This is in sharp contrast with previous field studies of air-sea gas exchange, which showed that wind was the dominating forcing function. The results suggest that gas transfer parameterizations that rely solely on wind will be insufficient for regions with low to intermediate winds and strong insolation.
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ArticleInorganic carbon and pCO(2) variability during ice formation in the Beaufort Gyre of the Canada Basin.(American Geophysical Union, 2019-05-07) DeGrandpre, Michael D. ; Lai, Chun-Ze ; Timmermans, Mary-Louise ; Krishfield, Richard A. ; Proshutinsky, Andrey ; Torres, Daniel J.Solute exclusion during sea ice formation is a potentially important contributor to the Arctic Ocean inorganic carbon cycle that could increase as ice cover diminishes. When ice forms, solutes are excluded from the ice matrix, creating a brine that includes dissolved inorganic carbon (DIC) and total alkalinity (AT). The brine sinks, potentially exporting DIC and AT to deeper water. This phenomenon has rarely been observed, however. In this manuscript, we examine a ~1 year pCO2 mooring time series where a ~35‐μatm increase in pCO2 was observed in the mixed layer during the ice formation period, corresponding to a simultaneous increase in salinity from 27.2 to 28.5. Using salinity and ice based mass balances, we show that most of the observed increases can be attributed to solute exclusion during ice formation. The resulting pCO2 is sensitive to the ratio of AT and DIC retained in the ice and the mixed layer depth, which controls dilution of the ice‐derived AT and DIC. In the Canada Basin, of the ~92 μmol/kg increase in DIC, 17 μmol/kg was taken up by biological production and the remainder was trapped between the halocline and the summer stratified surface layer. Although not observed before the mooring was recovered, this inorganic carbon was likely later entrained with surface water, increasing the pCO2 at the surface. It is probable that inorganic carbon exclusion during ice formation will have an increasingly important influence on DIC and pCO2 in the surface of the Arctic Ocean as seasonal ice production and wind‐driven mixing increase with diminishing ice cover.
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ArticleBiases in the air-sea flux of CO2 resulting from ocean surface temperature gradients(American Geophysical Union, 2004-06-30) Ward, Brian ; Wanninkhof, Rik ; McGillis, Wade R. ; Jessup, Andrew T. ; DeGrandpre, Michael D. ; Hare, Jeffrey E. ; Edson, James B.The difference in the fugacities of CO2 across the diffusive sublayer at the ocean surface is the driving force behind the air-sea flux of CO2. Bulk seawater fugacity is normally measured several meters below the surface, while the fugacity at the water surface, assumed to be in equilibrium with the atmosphere, is measured several meters above the surface. Implied in these measurements is that the fugacity values are the same as those across the diffusive boundary layer. However, temperature gradients exist at the interface due to molecular transfer processes, resulting in a cool surface temperature, known as the skin effect. A warm layer from solar radiation can also result in a heterogeneous temperature profile within the upper few meters of the ocean. Here we describe measurements carried out during a 14-day study in the equatorial Pacific Ocean (GasEx-2001) aimed at estimating the gradients of CO2 near the surface and resulting flux anomalies. The fugacity measurements were corrected for temperature effects using data from the ship's thermosalinograph, a high-resolution profiler (SkinDeEP), an infrared radiometer (CIRIMS), and several point measurements at different depths on various platforms. Results from SkinDeEP show that the largest cool skin and warm layer biases occur at low winds, with maximum biases of −4% and +4%, respectively. Time series ship data show an average CO2 flux cool skin retardation of about 2%. Ship and drifter data show significant CO2 flux enhancement due to the warm layer, with maximums occurring in the afternoon. Temperature measurements were compared to predictions based on available cool skin parameterizations to predict the skin-bulk temperature difference, along with a warm layer model.
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ArticleMeasuring Protons with Photons: A Hand-Held, Spectrophotometric pH Analyzer for Ocean Acidification Research, Community Science and Education(MDPI, 2022-10-18) Pardis, William ; Grabb, Kalina C. ; DeGrandpre, Michael D. ; Spaulding, Reggie ; Beck, James ; Pfeifer, Jonathan A. ; Long, David M.Ocean Acidification (OA) is negatively affecting the physiological processes of marine organisms, altering biogeochemical cycles, and changing chemical equilibria throughout the world’s oceans. It is difficult to measure pH broadly, in large part because accurate pH measurement technology is expensive, bulky, and requires technical training. Here, we present the development and evaluation of a hand-held, affordable, field-durable, and easy-to-use pH instrument, named the pHyter, which is controlled through a smartphone app. We determine the accuracy of pH measurements using the pHyter by comparison with benchtop spectrophotometric seawater pH measurements, measurement of a certified pH standard, and comparison with a proven in situ instrument, the iSAMI-pH. These results show a pHyter pH measurement accuracy of ±0.046 pH or better, which is on par with interlaboratory seawater pH measurement comparison experiments. We also demonstrate the pHyter’s ability to conduct both temporal and spatial studies of coastal ecosystems by presenting data from a coral reef and a bay, in which the pHyter was used from a kayak. These studies showcase the instrument’s portability, applicability, and potential to be used for community science, STEM education, and outreach, with the goal of empowering people around the world to measure pH in their own backyards.
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ArticleSupplement to physical exchanges at the air–sea interface : UK–SOLAS field measurements(American Meteorological Society, 2009-05) Brooks, Ian M. ; Yelland, Margaret J. ; Upstill-Goddard, Robert C. ; Nightingale, Philip D. ; Archer, Stephen D. ; D'Asaro, Eric A. ; Beale, Rachael ; Beatty, Cory ; Blomquist, Byron ; Bloom, A. Anthony ; Brooks, Barbara J. ; Cluderay, John ; Coles, David ; Dacey, John W. H. ; DeGrandpre, Michael D. ; Dixon, Jo ; Drennan, William M. ; Gabriele, Joseph ; Goldson, Laura E. ; Hardman-Mountford, Nick ; Hill, Martin K. ; Horn, Matt ; Hsueh, Ping-Chang ; Huebert, Barry ; De Leeuw, Gerrit ; Leighton, Timothy G. ; Liddicoat, Malcolm ; Lingard, Justin J. N. ; McNeil, Craig L. ; McQuaid, James B. ; Moat, Bengamin I. ; Moore, Gerald ; Neill, Craig L. ; Norris, Sarah J. ; O'Doherty, Simon ; Pascal, Robin W. ; Prytherch, John ; Rebozo, Mike ; Sahlee, Erik ; Salter, Matt ; Schuster, Ute ; Skjelvan, Ingunn ; Slagter, Hans ; Smith, Michael H. ; Smith, Paul D. ; Srokosz, Meric ; Stephens, John A. ; Taylor, Peter K. ; Telszewski, Maciej ; Walsh, Roisin ; Ward, Brian ; Woolf, David K. ; Young, Dickon ; Zemmelink, Hendrik J.
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ArticleInvestigations of air-sea gas exchange in the CoOP Coastal Air-Sea Chemical Exchange project(Oceanography Society, 2008-12) Edson, James B. ; DeGrandpre, Michael D. ; Frew, Nelson M. ; McGillis, Wade R.The exchange of CO2 and other gases across the ocean-air interface is an extremely important component in global climate dynamics, photosynthesis and respiration, and the absorption of anthropogenically produced CO2. The many different mechanisms and properties that control the air-sea flux of CO2 can have large spatial and temporal variability, particularly in the coastal environment. The need for making short-time-scale and small-spatial-scale estimates of gas transfer velocity, along with the physical and chemical parameters that affect it, provided a framework for the field experiments of the Coastal Ocean Processes Program (CoOP) Coastal Air-Sea Chemical Exchange (CASCEX) program. As such, the CASCEX project provided an opportunity to develop some of the first in situ techniques to estimate gas fluxes using micrometeorological and thermal imagery techniques. The results reported from the CASCEX experiments represent the first step toward reconciling the indirect but widely accepted estimates of gas exchange with these more direct, higher-resolution estimates over the coastal ocean. These results and the advances in sensor technology initiated during the CASCEX project have opened up even larger regions of the global ocean to investigation of gas exchange and its role in climate change.
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ArticleOcean time series observations of changing marine ecosystems: An era of integration, synthesis, and societal applications(Frontiers Media, 2019-07-12) Benway, Heather M. ; Lorenzoni, Laura ; White, Angelicque E. ; Fiedler, Björn ; Levine, Naomi M. ; Nicholson, David P. ; DeGrandpre, Michael D. ; Sosik, Heidi M. ; Church, Matthew J. ; O'Brien, Todd D. ; Leinen, Margaret S. ; Weller, Robert A. ; Karl, David M. ; Henson, Stephanie A. ; Letelier, Ricardo M.Sustained ocean time series are critical for characterizing marine ecosystem shifts in a time of accelerating, and at times unpredictable, changes. They represent the only means to distinguish between natural and anthropogenic forcings, and are the best tools to explore causal links and implications for human communities that depend on ocean resources. Since the inception of sustained ocean observations, ocean time series have withstood many challenges, most prominently availability of uninterrupted funding and retention of trained personnel. This OceanObs’19 review article provides an overarching vision for sustained ocean time series observations for the next decade, focusing on the growing challenges of maintaining sustained ocean time series, including ship-based and autonomous coastal and open-ocean platforms, as well as remote sensing. In addition to increased diversification of funding sources to include the private sector, NGOs, and other groups, more effective engagement of stakeholders and other end-users will be critical to ensure the sustainability of ocean time series programs. Building a cohesive international time series network will require dedicated capacity to coordinate across observing programs and leverage existing infrastructure and platforms of opportunity. This review article outlines near-term observing priorities and technology needs; explores potential mechanisms to broaden ocean time series data applications and end-user communities; and describes current tools and future requirements for managing increasingly complex multi-platform data streams and developing synthesis products that support science and society. The actionable recommendations outlined herein ultimately form the basis for a robust, sustainable, fit-for-purpose time series network that will foster a predictive understanding of changing ocean systems for the benefit of society.
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ArticlePhysical exchanges at the air–sea interface : UK–SOLAS field measurements(American Meteorological Society, 2009-05) Brooks, Ian M. ; Bloom, A. Anthony ; Brooks, Barbara J. ; Lingard, Justin J. N. ; McQuaid, James B. ; Norris, Sarah J. ; Smith, Michael H. ; Smith, Paul D. ; Yelland, Margaret J. ; Moat, Bengamin I. ; Pascal, Robin W. ; Prytherch, John ; Srokosz, Meric ; Taylor, Peter K. ; Upstill-Goddard, Robert C. ; Salter, Matt ; Nightingale, Philip D. ; Archer, Stephen D. ; Beale, Rachael ; Dixon, Jo ; Goldson, Laura E. ; Hardman-Mountford, Nick ; Liddicoat, Malcolm ; Moore, Gerald ; Stephens, John A. ; D'Asaro, Eric A. ; McNeil, Craig L. ; Beatty, Cory ; DeGrandpre, Michael D. ; Blomquist, Byron ; Huebert, Barry ; Cluderay, John ; Zemmelink, Hendrik J. ; Coles, David ; Hsueh, Ping-Chang ; Leighton, Timothy G. ; Dacey, John W. H. ; Drennan, William M. ; Rebozo, Mike ; Sahlee, Erik ; Gabriele, Joseph ; Hill, Martin K. ; Horn, Matt ; De Leeuw, Gerrit ; Neill, Craig ; Skjelvan, Ingunn ; O'Doherty, Simon ; Walsh, Roisin ; Young, Dickon ; Schuster, Ute ; Telszewski, Maciej ; Slagter, Hans ; Ward, Brian ; Woolf, David K.As part of the U.K. contribution to the international Surface Ocean–Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosol-size spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.