Sources of dissolved inorganic carbon to the Canada Basin halocline : a multitracer study

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 2918–2936, doi:10.1002/2015JC011535.We examine the dissolved inorganic carbon maximum in the Canada Basin halocline using a suite of geochemical tracers to gain insight into the factors that contribute to the persistence of this feature. Hydrographic and geochemical samples were collected in the upper 500 m of the southwestern Canada Basin water column in the summer of 2008 and fall of 2009. These observations were used to identify conservative and nonconservative processes that contribute dissolved inorganic carbon to halocline source waters, including shelf sediment organic matter remineralization, air-sea gas exchange, and sea-ice brine export. Our results indicate that the remineralization of organic matter that occurs along the Bering and Chukchi Sea shelves is the overwhelming contributor of dissolved inorganic carbon to Pacific Winter Water that occupies the middle halocline in the southwestern Canada Basin. Nonconservative contributions from air-sea exchange and sea-ice brine are not significant. The broad salinity range associated with the DIC maximum, compared to the narrow salinity range of the nutrient maximum, is due to mixing between Pacific and Atlantic water and not abiotic addition of DIC.NSERC; Fisheries and Oceans Canada; US National Science Foundation Office of Polar Programs Grant Number: OPP-0424864; Canadian International Polar Year Office2016-11-0

The distribution of methylated sulfur compounds, DMS and DMSP, in Canadian subarctic and Arctic marine waters during summer 2015

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Biogeosciences 15 (2018): 2449–2465, doi:10.5194/bg-15-2449-2018.We present seawater concentrations of dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) measured across a transect from the Labrador Sea to the Canadian Arctic Archipelago during summer 2015. Using an automated ship-board gas chromatography system and a membrane-inlet mass spectrometer, we measured a wide range of DMS (∼ 1 to 18 nM) and DMSP (∼ 1 to 150 nM) concentrations. The highest DMS and DMSP concentrations occurred in a localized region of Baffin Bay, where surface waters were characterized by high chlorophyll a (chl a) fluorescence, indicative of elevated phytoplankton biomass. Across the full sampling transect, there were only weak relationships between DMS(P), chl a fluorescence and other measured variables, including positive relationships between DMSP : chl a ratios and several taxonomic marker pigments, and elevated DMS(P) concentrations in partially ice-covered areas. Our high spatial resolution measurements allowed us to examine DMS variability over small scales (< 1 km), documenting strong DMS concentration gradients across surface hydrographic frontal features. Our new observations fill in an important observational gap in the Arctic Ocean and provide additional information on sea–air DMS fluxes from this ocean region. In addition, this study constitutes a significant contribution to the existing Arctic DMS(P) dataset and provides a baseline for future measurements in the region.This work was supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) through the Climate Change and Atmospheric Research program (Arctic-GEOTRACES)

Patterns and drivers of dimethylsulfide concentration in the northeast subarctic Pacific across multiple spatial and temporal scales.

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution 4.0 License. The definitive version was published in Biogeosciences 16(8), (2019):1729-1754, doi:10.5194/bg-16-1729-2019.The northeast subarctic Pacific (NESAP) is a globally important source of the climate-active gas dimethylsulfide (DMS), yet the processes driving DMS variability across this region are poorly understood. Here we examine the spatial distribution of DMS at various spatial scales in contrasting oceanographic regimes of the NESAP. We present new high-spatial-resolution measurements of DMS across hydrographic frontal zones along the British Columbia continental shelf, together with key environmental variables and biological rate measurements. We combine these new data with existing observations to produce a revised summertime DMS climatology for the NESAP, yielding a broader context for our sub-mesoscale process studies. Our results demonstrate sharp DMS concentration gradients across hydrographic frontal zones and suggest the presence of two distinct DMS cycling regimes in the NESAP, corresponding to microphytoplankton-dominated waters along the continental shelf and nanoplankton-dominated waters in the cross-shelf transitional zone. DMS concentrations across the continental shelf transition (range < 1–10 nM, mean 3.9 nM) exhibited positive correlations to salinity (r=0.80), sea surface height anomaly (SSHA; r=0.51), and the relative abundance of prymnesiophyte and dinoflagellates (r=0.89). In contrast, DMS concentrations in nearshore coastal transects (range < 1–24 nM, mean 6.1 nM) showed a negative correlation with salinity (r=−0.69; r=−0.78) and SSHA (r=−0.81; r=−0.75) and a positive correlation to relative diatom abundance (r=0.88; r=0.86). These results highlight the importance of bloom-driven DMS production in continental shelf waters of this region and the role of prymnesiophytes and dinoflagellates in DMS cycling further offshore. In all areas, the rate of DMS consumption appeared to be an important control on observed concentration gradients, with higher DMS consumption rate constants associated with lower DMS concentrations. We compiled a data set of all available summertime DMS observations for the NESAP (including previously unpublished results) to examine the performance of several existing algorithms for predicting regional DMS concentrations. None of these existing algorithms was able to accurately reproduce observed DMS distributions across the NESAP, although performance was improved by the use of regionally tuned coefficients. Based on our compiled observations, we derived an average summertime distribution map for DMS concentrations and sea–air fluxes across the NESAP, estimating a mean regional flux of 0.30 Tg of DMS-derived sulfur to the atmosphere during the summer season.We dedicate this article to the memory of Ronald P. Kiene, a wonderful scientist, mentor and friend. His contributions to DMS and DMSP research have shaped our field over the past 3 decades, and he will be missed by many around the world. We also wish to thank many individuals involved in data collection and logistical aspects of the cruises presented here, including scientists from the Institute of Ocean Sciences, the captain and crew of the R/V Oceanus and the CCGS John P. Tully, and members of the Tortell, Kiene, Levine and Hatton laboratory groups. We also thank Theodore Ahlvin for GIS support and both reviewers for their insightful comments. Support for this work was provided from the US National Science Foundation (grant no. 1436344) and from the Natural Sciences and Engineering Research Council of Canada

Concentrations and cycling of DMS, DMSP, and DMSO in coastal and offshore waters of the Subarctic Pacific during summer, 2010-2011

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 3269–3286, doi:10.1002/2016JC012465.Concentrations of dimethylsulfide (DMS), measured in the Subarctic Pacific during summer 2010 and 2011, ranged from ∼1 to 40 nM, while dissolved dimethylsulfoxide (DMSO) concentrations (range 13-23 nM) exceeded those of dissolved dimethyl sulfoniopropionate (DMSP) (range 1.3–8.8 nM). Particulate DMSP dominated the reduced sulfur pool, reaching maximum concentrations of 100 nM. Coastal and off shore waters exhibited similar overall DMS concentration ranges, but sea-air DMS fluxes were lower in the oceanic waters due to lower wind speeds. Surface DMS concentrations showed statistically significant correlations with various hydrographic variables including the upwelling intensity (r2 = 0.52, p < 0.001) and the Chlorophyll a/mixed layer depth ratio (r2 = 0.52, p < 0.001), but these relationships provided little predictive power at small scales. Stable isotope tracer experiments indicated that the DMSP cleavage pathway always exceeded the DMSO reduction pathway as a DMS source, leading to at least 85% more DMS production in each experiment. Gross DMS production rates were positively correlated with the upwelling intensity, while net rates of DMS production were significantly correlated to surface water DMS concentrations. This latter result suggests that our measurements captured dominant processes driving surface DMS accumulation across a coastal-oceanic gradient.Natural Sciences and Engineering Research Council of Canada, from the Peter Wall Institute for Advanced Studies2017-10-2

Biological and physical controls on N2, O2, and CO2 distributions in contrasting Southern Ocean surface waters

We present measurements of pCO2, O2 concentration, biological oxygen saturation (ΔO2/Ar), and N2 saturation (ΔN2) in Southern Ocean surface waters during austral summer, 2010–2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chl a) concentrations in regions of frontal mixing and sea ice melt. pCO2 and ΔO2/Ar exhibited large spatial gradients (range 90 to 450 µatm and −10 to 60%, respectively) and covaried strongly with Chl a. However, the ratio of biological O2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time scales of O2 and CO2 air-sea equilibration. We measured significant oceanic CO2 uptake, with a mean air-sea flux (~ −10 mmol m−2 d−1) that significantly exceeded regional climatological values. N2 was mostly supersaturated in surface waters (mean ΔN2 of +2.5%), while physical processes resulted in both supersaturation and undersaturation of mixed layer O2 (mean ΔO2phys = 2.1%). Box model calculations were able to reproduce much of the spatial variability of ΔN2 and ΔO2phys along the cruise track, demonstrating significant effects of air-sea exchange processes (e.g., atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface ΔO2/Ar data, ranged from ~ −40 to > 300 mmol O2 m−2 d−1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and stratified regions of sea ice melt, reflecting physical controls on surface water light fields and nutrient availability

Vertical structure, seasonal drawdown, and net community production in the Ross Sea, Antarctica

We calculate net community production (NCP) during summer 2005-2006 and spring 2006 in the Ross Sea using multiple approaches to determine the magnitude and consistency of rates. Water column carbon and nutrient inventories and surface ocean O-2/Ar data are compared to satellite-derived primary productivity (PP) estimates and C-14 uptake experiments. In spring, NCP was related to stratification proximal to upper ocean fronts. In summer, the most intense C drawdown was in shallow mixed layers affected by ice melt; depth-integrated C drawdown, however, increased with mixing depth. Delta O-2/Ar-based methods, relying on gas exchange reconstructions, underestimate NCP due to seasonal variations in surface Delta O-2/Ar and NCP rates. Mixed layer Delta O-2/Ar requires approximately 60 days to reach steady state, starting from early spring. Additionally, cold temperatures prolong the sensitivity of gas exchange reconstructions to past NCP variability. Complex vertical structure, in addition to the seasonal cycle, affects interpretations of surface-based observations, including those made from satellites. During both spring and summer, substantial fractions of NCP were below the mixed layer. Satellite-derived estimates tended to overestimate PP relative to C-14-based estimates, most severely in locations of stronger upper water column stratification. Biases notwithstanding, NCP-PP comparisons indicated that community respiration was of similar magnitude to NCP. We observed that a substantial portion of NCP remained as suspended particulate matter in the upper water column, demonstrating a lag between production and export. Resolving the dynamic physical processes that structure variance in NCP and its fate will enhance the understanding of the carbon cycling in highly productive Antarctic environments

CO2 Sensitivity of Southern Ocean Phytoplankton

The Southern Ocean exerts a strong impact on marine biogeochemical cycles and global air-sea CO2 fluxes. Over the coming century, large increases in surface ocean CO2 levels, combined with increased upper water column temps. and stratification, are expected to diminish Southern Ocean CO2 uptake. These effects could be significantly modulated by concomitant CO2-dependent changes in the region\u27s biol. carbon pump. Here we show that CO2 concentrations affect the physiology, growth and species composition. of phytoplankton assemblages in the Ross Sea, Antarctica. Field results from in situ sampling and ship-board incubation experiments demonstrate that inorganic carbon uptake, steady-state productivity and diatom species composition are sensitive to CO2 concentrations ranging from 100 to 800 ppm. Elevated CO2 led to a measurable increase in phytoplankton productivity, promoting the growth of larger chain-forming diatoms. Our results suggest that CO2 concentrations can influence biological carbon cycling in the Southern Ocean, thereby creating potential climate feedbacks

Interannual Variability in Methane and Nitrous Oxide Concentrations and Sea-Air Fluxes Across the North American Arctic Ocean (2015–2019)

Between 2015 and 2018, we collected approximately 2,000 water column measurements of methane (CH4) and nitrous oxide (N2O) concentrations in the North American Arctic Ocean during summer and early fall. We also obtained 25 measurements of CH4 and N2O concentrations in rivers along the Northwest Passage and Ellesmere Island in midsummer 2017–2019. Our results show that N2O is generated in the highly productive Bering and Chukchi Seas and transported northeastward, producing a persistent subsurface N2O peak in the Beaufort Sea. The Chukchi and Beaufort Sea sediments are a significant source of CH4 to the water column. These sedimentary sources and associated water column consumption display significant spatial gradients and interannual variability. CH4 isotope data demonstrate the importance of CH4 oxidation across the study region. We find that rivers are not a significant source of CH4 or N2O to the Arctic Ocean at the time of year sampled. The estimated annual sea-air flux across the study region (2.3 million km2) had a median (first quartile, third quartile) of 0.009 (0.002, 0.023) Tg CH4 y−1 and −0.003 (−0.013, 0.010) Tg N y−1. These results suggest that the North American Arctic Ocean currently plays a negligible role in global CH4 and N2O budgets. Our expansive data set, with observations at many repeat stations, provides a synopsis of present-day Arctic CH4 and N2O distributions and their range of variability, as well as a benchmark against which future climatedependent changes can be evaluated

Gross and net production during the spring bloom along the Western Antarctic Peninsula

Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of New Phytologist Trust for personal use, not for redistribution. The definitive version was published in New Phytologist 205 (2015): 182-191, doi:10.1111/nph.13125.This study explores some of the physiological mechanisms responsible for high productivity near the shelf in the Western Antarctic Peninsula despite a short growing season and cold temperature. We measured gross and net primary production at Palmer Station during the summer 2012/2013 via three different techniques: 1) incubation with H218O; 2) incubation with 14CO2; and 3) in situ measurements of O2/Ar and triple oxygen isotope. Additional laboratory experiments were performed with the psychrophilic diatom Fragilariopsis cylindrus. During the spring bloom, which accounted for more than half of the seasonal gross production at Palmer Station, the ratio of net to gross production reached a maximum greater than ~60%, among the highest ever reported. The use of multiple-techniques showed that these high ratios resulted from low heterotrophic respiration and very low daylight autotrophic respiration. Laboratory experiments revealed a similar ratio of net to gross O2 production in F.cylindrus and provided the first experimental evidence for an important level of cyclic electron flow (CEF) in this organism. The low ratio of community respiration to gross primary production observed during the bloom at Palmer Station may be characteristic of high latitude coastal ecosystems and partially supported by a very active CEF in psychrophilic phytoplankton.This study was supported by funds from the US National Science Foundation (Award numbers 1040965 and 1043593). Funding to PDT was provided by the Natural Science and Engineering Research Council of Canada

Metabolic balance of coastal Antarctic waters revealed by autonomous pCO2 and ΔO2/Ar measurements

Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 41 (2014): 6803–6810, doi:10.1002/2014GL061266.We use autonomous gas measurements to examine the metabolic balance (photosynthesis minus respiration) of coastal Antarctic waters during the spring/summer growth season. Our observations capture the development of a massive phytoplankton bloom and reveal striking variability in pCO2 and biological oxygen saturation (ΔO2/Ar) resulting from large shifts in community metabolism on time scales ranging from hours to weeks. Diel oscillations in surface gases are used to derive a high-resolution time series of net community production (NCP) that is consistent with 14C-based primary productivity estimates and with the observed seasonal evolution of phytoplankton biomass. A combination of physical mixing, grazing, and light availability appears to drive variability in coastal Antarctic NCP, leading to strong shifts between net autotrophy and heterotrophy on various time scales. Our approach provides insight into the metabolic responses of polar ocean ecosystems to environmental forcing and could be employed to autonomously detect climate-dependent changes in marine primary productivity.This study was supported by funds from the U.S. National Science Foundation (OPP awards ANT-0823101, ANT-1043559, ANT-1043593, and ANT-1043532) as well as support for PDT and ECA from the National Science and Engineering Research Council of Canada.2015-04-0