72 research outputs found
Influence of biological carbon export on ocean carbon uptake over the annual cycle across the North Pacific Ocean
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 Global Biogeochemical Cycles 31 (2017): 81â95, doi:10.1002/2016GB005527.We evaluate the influences of biological carbon export, physical circulation, and temperature-driven solubility changes on air-sea CO2 flux across the North Pacific basin (35°Nâ50°N, 142°Eâ125°W) throughout the full annual cycle by constructing mixed layer budgets for dissolved inorganic carbon (DIC) and pCO2, determined on 15 container ship transects between Hong Kong and Long Beach, CA, from 2008 to 2012. Annual air-sea CO2 flux is greatest in the western North Pacific and decreases eastward across the basin (2.7â±â0.9âmolâCâmâ2âyrâ1 west of 170°E, as compared to 2.1â±â0.3âmolâCâmâ2âyrâ1 east of 160°W). East of 160°W, DIC removal by annual net community production (NCP) more than fully offsets the DIC increase due to air-sea CO2 flux. However, in the region west of 170°E influenced by deep winter mixing, annual NCP only offsets ~20% of the DIC increase due to air-sea CO2 flux, requiring significant DIC removal by geostrophic advection. Temperature-driven solubility changes have no net influence on pCO2 and account for <25% of annual CO2 uptake. The seasonal timing of NCP strongly affects its influence on air-sea CO2 flux. Biological carbon export from the mixed layer has a stronger influence on pCO2 in summer when mixed layers are shallow, but changes in pCO2 have a stronger influence on air-sea CO2 flux in winter when high wind speeds drive more vigorous gas exchange. Thus, it is necessary to determine the seasonal timing as well as the annual magnitude of NCP to determine its influence on ocean carbon uptake.NDSEG Fellowship from the Office of Naval Research;
NSF Graduate Research Fellowship;
NSF Ocean Sciences Grant Numbers: 0628663, 1259055;
NOAA Climate Program Office Grant Number: A10OAR43100882017-07-2
Evidence of O2 consumption in underway seawater lines: Implications for air-sea O2 and CO2 fluxes
We observed O2 deficits of 0.5 to 2.0% (1 to 4 mol/kg) in the underway seawater lines of three different ships. Deficits in O2/Ar and isotopic enrichments in dissolved O2 observed in underway seawater lines indicate a respiratory removal process. A 1% respiratory bias in underway lines would lead to a 2.5-5 atm (2.5-5pbar) enhancement in surface water pCO2. If an underway pCO2 bias of this magnitude affectedall measurements, the global oceanic carbon uptake based on pCO 2 climatologies would be 0.5-0.8 Pg/yr higher than the present estimate of 1.6 Pg/yr. Treatment of underway lines with bleach for several hours and thorough flushing appeared to minimize O2 loss. Given the increasing interest in underway seawater measurements for the determination of surface CO2 and O2 fluxes, respiration in underway seawater lines must be identified and eliminated on all observing ships to ensure unbiased data
Redfield ratios revisited: Removing the biasing effect of anthropogenic CO2
Redfield ratios of remineralization are calculated based on chemical data analysis on isopycnal surfaces. The concentrations of dissolved inorganic carbon used in this study were corrected for the anthropogenic CO2 content as estimated with a back-calculation technique. The corrections increased the apparent carbon remineralization by 25-30%, thus proving important for the reliable estimation of Redfield carbon ratios in the presence of anthropogenic CO2. Best estimates from this study largely confirm the more recently published Redfield ratios of remineralization. The following results were obtained for the latitude range 3-41°N along 20-29°W in the Northeast Atlantic Ocean: Corg: P ratio = 123 ± 10; Corg : N ratio = 7.2 ± 0.8; -O2 :Corg ratio = 1.34 ± 0.06; -O2 : P ratio = 165 ± 15; N: P ratio = 17.5 ± 2.0. These ratios are in close agreement with the average composition of phytoplankton and represent respiration of organic matter consisting on average of 52% protein, 36% polysaccharide, and 12% lipid
Discrepant estimates of primary and export production from satellite algorithms, a biogeochemical model, and geochemical tracer measurements in the North Pacific Ocean
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 Geophysical Research Letters 43 (2016): 8645â8653, doi:10.1002/2016GL070226.Estimates of primary and export production (PP and EP) based on satellite remote sensing algorithms and global biogeochemical models are widely used to provide year-round global coverage not available from direct observations. However, observational data to validate these approaches are limited. We find that no single satellite algorithm or model can reproduce seasonal and annual geochemically determined PP, export efficiency (EP/PP), and EP rates throughout the North Pacific basin, based on comparisons throughout the full annual cycle at time series stations in the subarctic and subtropical gyres and basin-wide regions sampled by container ship transects. The high-latitude regions show large PP discrepancies in winter and spring and strong effects of deep winter mixed layers on annual EP that cannot be accounted for in current satellite-based approaches. These results underscore the need to evaluate satellite- and model-based estimates using multiple productivity parameters measured over broad ocean regions throughout the annual cycle.NDSEG Fellowship from the Office of Naval Research;
NSF Graduate Research Fellowship;
ARCS Foundation Fellowship2017-02-2
Synoptic Mesoscale to Basin Scale Variability in Biological Productivity and Chlorophyll in the Kuroshio Extension Region
The Kuroshio current separates from the Japanese coast to become the eastward flowing Kuroshio Extension (KE) characterized by a strong latitudinal density front, high levels of mesoscale (eddy) energy, and high chlorophyll a (Chl). While satellite measurements of Chl show evidence of the impact of mesoscale eddies on the standing stock of phytoplankton, there have been very limited synoptic, spatially resolved in situ estimates of productivity in this region. Here, we present underway measurements of oxygen/argon supersaturation (ÎO2/Ar), a tracer of net biological productivity, for the KE made in spring, summer, and early autumn. We find large seasonal differences in the relationships between ÎO2/Ar, Chl, and sea level anomaly (SLA), a proxy for local thermocline depth deviations driven by mesoscale eddies derived from satellite observations. We show that the KE is a pronounced hotspot of high ÎO2/Ar in spring, but corresponding surface Chl values are low and have no correlation with ÎO2/Ar. In summer, there is a hotspot of productivity associated with the Oyashio front, where ÎO2/Ar and Chl are strongly positively correlated. In autumn, ÎO2/Ar and Chl are consistently low throughout the region and also positively correlated. By combining our analysis of the in situ ÎO2/Ar data with complementary Argo, BGC-Argo, repeat hydrography, and SLA observations, we infer the combination of physical and biological controls that drive the observed distributions of ÎO2/Ar and Chl. We find that the KE and Oyashio currents both act to supply nutrients laterally, fueling regions of high productivity in spring and summer, respectively
The annual cycle of gross primary production, net community production, and export efficiency across the North Pacific Ocean
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 Global Biogeochemical Cycles 30 (2016): 361â380, doi:10.1002/2015GB005318.We measured triple oxygen isotopes and oxygen/argon dissolved gas ratios as nonincubation-based geochemical tracers of gross oxygen production (GOP) and net community production (NCP) on 16 container ship transects across the North Pacific from 2008 to 2012. We estimate rates and efficiency of biological carbon export throughout the full annual cycle across the North Pacific basin (35°Nâ50°N, 142°Eâ125°W) by constructing mixed layer budgets that account for physical and biological influences on these tracers. During the productive season from spring to fall, GOP and NCP are highest in the Kuroshio region west of 170°E and decrease eastward across the basin. However, deep winter mixed layers (>200âm) west of 160°W ventilate ~40â90% of this seasonally exported carbon, while only ~10% of seasonally exported carbon east of 160°W is ventilated in winter where mixed layers are <120âm. As a result, despite higher annual GOP in the west than the east, the annual carbon export (sequestration) rate and efficiency decrease westward across the basin from export of 2.3â±â0.3âmolâCâmâ2âyrâ1 east of 160°W to 0.5â±â0.7âmolâCâmâ2âyrâ1 west of 170°E. Existing productivity rate estimates from time series stations are consistent with our regional productivity rate estimates in the eastern but not western North Pacific. These results highlight the need to estimate productivity rates over broad spatial areas and throughout the full annual cycle including during winter ventilation in order to accurately estimate the rate and efficiency of carbon sequestration via the ocean's biological pump.This work was funded by a NDSEG Fellowship from the Office of Naval Research, a NSF Graduate Research Fellowship, and an ARCS Foundation Fellowship to H.I.P. and by NSF Ocean Sciences (0628663 and 1259055 to P.D.Q.).2016-08-2
Relationship between anthropogenic CO<sub>2</sub> and the 13C Suess effect in the North Atlantic Ocean
Temporal trends in oceanic dissolved inorganic carbon (DIC) and ÎŽ13C-DIC were reconstructed along five isopycnals in the upper 1000 m of the North Atlantic Ocean using a back-calculation approach. The mean anthropogenic DIC increase was 1.21 ± 0.07 ÎŒmol kgâ1 yrâ1 and the mean 13C decrease was â0.026 ± 0.002â° yrâ1, both in good agreement with the results from previous studies. The observed ÎŽ13C-DIC perturbation ratio is â0.024 ± 0.003â° (ÎŒmol kgâ1)â1. Our results indicate that the North Atlantic is able to maintain equilibrium with the anthropogenic perturbation for DIC and follows it with decadal time lag for ÎŽ13C. A CFC-calibrated one-dimensional isopycnal advection-diffusion model is used to evaluate temporal DIC and ÎŽ13C trends and perturbation ratios of the reconstructions. We investigate the time history of the air-sea CO2 and 13C disequilibria in the North Atlantic and discuss the importance of physical and biological processes in maintaining them. We find evidence that the North Atlantic Ocean is characterized by enhanced uptake of anthropogenic CO2. Also, we use the model to examine how the time rate of change of ÎŽ13C depends on changes in the temporal evolution of ÎŽ13C in the atmosphere. The model evolution explains the curious result that the time rate of change of surface water ÎŽ13C in the North Atlantic Ocean can exceed that observed concurrently in the atmosphere. Finally we introduce a powerful way of estimating the global air-sea pCO2 disequilibrium based on the oceanic ÎŽ13C-DIC perturbation ratio
Influence of a Cyclonic Eddy on Microheterotroph Biomass and Carbon Export in the Lee of Hawaii
[1] A multiâplatform sampling strategy was used to investigate carbon cycling in a coldâcore eddy that formed in the lee of Hawaii during September 2000. Microheterotroph biomass and 234Thâderived carbon export rates within the eddy were 2 to 3 times higher than those observed for adjacent waters. If this eddy is representative of other cyclonic eddies that are frequently formed in the lee of Hawaii, then eddy activity may significantly enhance the areal efficiency of the biological pump and facilitate the transfer of organic carbon to organisms inhabiting the mesopelagic and abyssalâbenthic zones of this subtropical ecosystem
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High-resolution estimates of net community production and air-sea COâ flux in the northeast Pacific
Rates of net community production (NCP) and air-sea COâ flux in the Northeast Pacific subarctic, transition zone and subtropical regions (22°Nâ50°N, 145°Wâ152°W) were determined on a cruise in AugustâSeptember 2008 by continuous measurement of surface values of the ratio of dissolved oxygen to argon (Oâ/Ar) and the partial pressure of COâ (pCOâ). These estimates were compared with simultaneous measurements of sea surface temperature (SST), chlorophyll-a (chl-a), flow cytometry, and discrete surface nutrient concentrations. NCP and COâ influx were greatest in the subarctic (45°Nâ50°N, 25.8 ± 4.6 and 4.1 ± 0.9 mmol C mâ»ÂČ dâ»Âč) and northern transition zone (40°Nâ45°N, 17.1 ± 4.4 and 2.1 ± 0.5 mmol C mâ»ÂČ dâ»Âč), with mean NCP âŒ6â8Ă greater than mean CO2 invasion (error estimates reflect 1 Ï confidence intervals). Contrastingly, the southern transition zone (32°Nâ40°N) and subtropics (22°Nâ32°N) had lower mean NCP (5.4 ± 1.8 and 8.1 ± 2.1 mmol C mâ»ÂČ dâ»Âč, respectively) and mean COâ efflux (3.0 ± 0.5 and 0.1 ± 0.0 mmol C mâ»ÂČ dâ»Âč, respectively). In the subarctic and transition zone, NCP was highly correlated with surface chl-a and COâ influx, indicating strong coupling between the biological pump and COâ uptake. Meridional trends in our NCP estimates in the transition zone and subtropics were similar to those for integrated summertime NCP along the cruise track determined using an upper ocean climatological carbon budget
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Physicochemical and biological controls on primary and net community production across northeast Pacific seascapes
The subarctic-subtropical transition zone in the North Pacific represents the second largest sink of
atmospheric carbon dioxide in the world ocean, yet the relative importance of physical and biological processes in
this uptake is debated. In a step toward understanding the spatiotemporal variability of environmental,
physiological, and ecological factors that contribute to the efficacy of the biological pump, near-continuous
measurements of net primary production (NPP), net community production (NCP), export efficiency
(NCP : NPP), and several physiological and ecological variables were collected across subarctic, transition, and
subtropical seascapes of the Northeast Pacific during August and September of 2008. Whereas hydrographic
variability (e.g., temperature, salinity, and mixed layer) dominated at basin scales, the effects were balanced or
subsumed by biomass or taxa effects within individual seascapes. Fluorescence diagnostics suggested that the
transition seascape was neither iron nor macronutrient limited. NPP and NCP were strongly spatially coupled in
both the transition (r = 0.70; p < 0.0001) and subtropics (r = 0.68, p < 0.0001); however, the strength of
individual drivers as determined through multiple linear regression (MLR) varied across seascapes. NPP in the
transition seascape was driven primarily by nano- and microphytoplankton biomass, whereas NCP appeared to
be driven by changes in salinity, temperature, and to a lesser degree, diatom-specific biomass. Although NPP was
low in the subtropics, mesoscale changes in hydrographical factors and shifts in community structure from picoto
microphytoplankton contributed to moderate NCP and high export efficiency. Spatial variability in the relative
importance of hydrography, phytoplankton community structure, and NPP in driving NCP illuminates regional
sensitivity of the biological pump to future climate conditions.This is the publisherâs final pdf. The published article is copyrighted by the Association for the Sciences of Limnology and Oceanography, Inc. and can be found at: http://www.aslo.org/lo/
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