Diagnosing Co 2 Fluxes in the Upwelling System off the Oregon Coast Printer-friendly Version Interactive Discussion Diagnosing Co 2 Fluxes in the Upwelling System off the Oregon Coast Diagnosing Co 2 Fluxes in the Upwelling System off the Oregon Coast Printer-friendly Version Interactive Discussion

This discussion paper is/has been under review for the journal Biogeosciences (BG). Please refer to the corresponding final paper in BG if available. Abstract It is generally known that the interplay between the carbon and nutrients supplied from subsurface waters via biological metabolism would determine the CO 2 fluxes in up-welling systems. However, quantificational assessment of such interplay is difficult because of the dynamic nature of both upwelling circulation and the associated biogeo-5 chemistry. In this study, the diagnosis approach based upon the carbon/nutrient mass balance in the Ocean-dominated Margin (OceMar) framework was applied to resolve the CO 2 fluxes in the well-known upwelling system in the US west coast off Oregon, using the data collected along two cross-shelf transects from the inner shelf to the open basin in spring/early summer 2007. Through examining the biological consumption on 10 top of the water mass mixing built upon the total alkalinity–salinity relationship, we successfully predicted and semi-analytically resolved the CO 2 fluxes showing strong uptakes from the atmosphere beyond the nearshore regions, primarily resulting from the higher utilization of nutrients relative to dissolved inorganic carbon (DIC) based on their concurrent inputs from the depth. On the other hand, we showed significant 15 CO 2 outgassing in the nearshore regions associated with intensified upwelling and minor biological consumption, where CO 2 fluxes could be simplified without considering DIC/nutrient consumption. We reasoned that our approach in conceptualizing OceMar would be in a steady state with balanced DIC and nutrients via both physical transport and biological alterations in comparable timescales.


Introduction
The contemporary coastal ocean, characterized by high primary productivity due primarily to the abundant nutrient inputs from both river plume and coastal upwelling, is generally seen as a significant CO 2 sink at the global scale (Borges et al., 2005;Cai et al., 2006;Chen and Borges, 2009;Laruelle et al., 2010;Borges, 2011;Cai, 2011;Figures Back Close Full cycle remains limited, leading to the unanswered question of why some coastal systems are sources while others are sinks of atmospheric CO 2 .In shaping the concept of the coastal ocean carbon study, we recently proposed a new framework, the Oceandominated Margin (OceMar), for mechanistically understanding the CO 2 source/sink nature of an ocean margin (Dai et al., 2013).This framework highlights the importance of the boundary process between the open ocean and the ocean margin, and proposes a semi-analytical diagnosis approach to resolve sea-air CO 2 fluxes.The approach invokes an establishment of the water mass mixing scheme in order to define the physical transport, or the conservative portion of carbon and nutrients from the adjacent open ocean; and the constraint of the biogeochemical alteration of these nonlocal inputs in the upper waters of ocean margins.The water mass mixing scheme is typically revealed using conservative chemical tracers such as total alkalinity (TAlk) and/or dissolved calcium ion (Ca 2+ ) to bypass identifications of end-members associated with individual water masses that often possess high complexity in any given oceanic regime.The constraint of the biogeochemical alteration can then be estimated as the difference between the predicted values based on conservative mixing between end-members and the field measured values.The relative consumption between dissolved inorganic carbon (DIC) and nutrients determines if DIC is in excess or in deficit relative to the off-site input.Such excess DIC will eventually be released to the atmosphere through air-sea CO 2 exchange.Using two large marginal seas, the South China Sea (SCS) and the Caribbean Sea (CS) as cases, we have successfully predicted, via evaluating DIC and nutrient mass balance, the CO 2 outgassing that is consistent with the field observations (Dai et al., 2013).However, the OceMar concept and the diagnosis approach have not been attested to upwelling systems that can be either sources (e.g., Friederich et al., 2002;Torres et al., 2003;Fransson et al., 2006) or sinks (e.g., Borges et al., 2002;Santana-Casiano et al., 2009;Evans et al., 2012) of atmospheric CO 2 .While it is generally known that the interplay between the nutrients and DIC supplied from subsurface waters via biological metabolism would determine the CO 2 fluxes in upwelling systems, quantificational assessment of such interplay is Introduction

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Full This study thus chose the well-known upwelling system in the US west coast off Oregon, to examine the CO 2 flux dynamics through our proposed mass balance approach associated with carbon/nutrient coupling.The system under study is featured by a relatively narrow shelf at the northern and southern portions and a direct link with the eastern North Pacific (eNP) offshore (Fig. 1).While strong equatorward winds in spring/summer drive offshore Ekman transport at the surface along the coastline, the carbon and nutrient-rich deep water is transported shoreward and upward over the shelf to compensate for the offshore transport in the surface layer (Allen et al., 1995;Federiuk and Allen, 1995).Outcrops of waters from the depth of 150-200 m are frequently observed in the nearshore on the Oregon shelf, where the surface partial pressure of CO 2 (pCO 2 ) can reach levels near 1000 µatm.This water is then transported offshore and along shore while the pCO 2 is drawn down by biological productivity to levels of ∼ 200 µatm, far below the atmospheric pCO 2 value (Hales et al., 2005(Hales et al., , 2012;;Feely et al., 2008;Evans et al., 2011).Such a dramatic decrease in seawater pCO 2 might be due to the fact that the complete utilization of the preformed nutrients in the upwelled waters exceeds their corresponding net DIC consumption, leading to the area off Oregon acting as a net sink of atmospheric CO 2 during the upwelling season (Hales et al., 2005).On the other hand, Evans et al. (2011) suggest that the spring/early summer undersaturated pCO 2 conditions in some offshore areas result from nonlocal productivity associated with the Columbia River (CR) plume, which transports ∼ 77 % of the total runoff from the western North America to the Pacific Ocean (Hickey, 1989).
In this context, the Oregon shelf in the upwelling season can be a potential OceMartype system with the majority of DIC and nutrients in the upper layer originating from nonlocal deep waters of the eNP, though riverine inputs might complicate the application of the OceMar framework.On the other hand, upper waters in offshore areas beyond the upwelling circulation on the Oregon shelf would be largely fed by on-site Introduction

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Full deep waters via diapycnal mixing such as vertical diffusion, with minor influence of the CR plume depending on the circulation and discharges.
2 Study area and data source

California Current system and upwelling circulation
The upwelling circulation off Oregon is linked with the eastern boundary current, the California Current (CC) occupying the open basin of the eNP (Barth et al., 2000).The CC is a board and weak surface current (0-300 m) which carries lowsalinity/temperature water equatorward from the subarctic Pacific.The deeper-lying California Undercurrent (200-500 m), which has relatively high salinity and temperature, originates in the eastern Equatorial Pacific and flows poleward inshore along the west coast of North America (Lynn and Simpson, 1987).The CC system is characterized by coastal upwelling in spring/summer, during which waters primarily composed of the CC is transported upward from the depth of 150-200 m towards the nearshore surface (Castro et al., 2001).Both field observations and modeling studies (Spitz et al., 2005, and references therein) show that the upwelling circulation pattern over the Oregon shelf differs significantly between north and south of Newport (Fig. 1).North of Newport between 45.0 • N and 45.5 • N with a relatively straight coastline and narrow shelf, the uniform bottom topography generally results in the typical upwelling situation with a southward coastal jet close to shore at Cascade Head (Fig. 1).Over the central Oregon shelf between 43.5 • N and 45.0 • N, the highly variable bottom topography over Heceta Bank (Fig. 1) largely influences the upwelling circulation, leading to a complex three-dimensional sociated with interactions of the wind-forced coastal currents with Cape Blanco (Fig. 1) (Gan and Allen, 2005, and references therein).

Data source
Our data sets were based on the online published carbonate system and nutrient data collected along two transects off Oregon during the first North American Carbon Program (NACP) West Coast Cruise in spring/early summer 2007 (http://cdiac.ornl.gov/oceans/Coastal/NACP_West.html; Feely et al., 2008;Feely and Sabine, 2011).Transect 4 (stations 25-33 from nearshore to offshore) is located off Newport, Oregon, while Transect 5 (station 41-35 from nearshore to offshore) is located off Crescent City near the Oregon-California border.The most offshore stations on both transects were located in the open basin of the eNP (Fig. 1).

Results and discussion
The region under study is highly dynamic potentially involving coastal upwelling, the CR plume and the pelagic waters mixed by various Pacific water masses (Hill and Wheeler, 2002).Instead of accounting all of the water masses contributing to the CC system, the mixing scheme in the upper waters along both transects was examined via the total alkalinity-salinity (TAlk-Sal) relationship obtained during the sampling period such as to make quantification of the conservative portion of carbon and nutrients possible.
The end-members were therefore defined under this relationship, which might have experienced physical or biological alterations from their original water masses such as the CR and the CC.Subsequently, the biologically consumed DIC and nutrients were quantified as the difference between their conservative values predicted from the derived end-member mixing and the corresponding field measurements.Finally, the CO 2 source/sink nature in the upper waters off Oregon was diagnosed via a mass Introduction

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Full balance approach by estimating the relative consumption between DIC and nutrients according to Dai et al. (2013).

Various mixing schemes in the upper 200 m waters off Oregon
In the upper 200 m waters with salinity lower than ∼ 34.0, the TAlk-Sal relationship displayed two general phases along Transect 4. One was the linear regression for waters with salinity lower than ∼ 32.0 (corresponding to the depth of ∼ 10-20 m), having an intercept of ∼ 1200 µmol kg −1 .This value agreed well with the observed TAlk of ∼ 1000 µmol kg −1 in the main stream of the CR (Park et al., 1969b;Evans et al., 2013).
The other was the linear regression for waters with salinity between ∼ 32.0 and ∼ 34.0 (corresponding to the depth of ∼ 200 m), where the smaller intercept of ∼ 500 µmol kg −1 implied a smaller contribution from the CR plume (Fig. 2a).Exceptions were observed at the shallowest station 25 (water depth ∼ 50 m) and the deepest station 33 (water depth ∼ 2900 m).The TAlk-Sal relationship completely followed the second phase for the upper 200 m waters at station 33 (Fig. 2a), suggesting a small fraction of the CR plume even in the surface waters of this outmost station on Transect 4. On the other hand, data points of the two parameters were not well correlated through the entire water column of station 25 and fell off either regression line (Fig. 2a).The water mass mixing at this innermost station was not as straightforward, despite minor freshwater admixture as suggested by the high surface salinity of > 32.0.
In contrast, all salinity values, including surface samples in the upper 200 m waters on Transect 5, were higher than 32.0 (Fig. 2b).The TAlk-Sal relationship also displayed two phases.One was the linear regression for stations 35-38 deeper than ∼ 800 m, with slope and intercept values comparable to the second phase observed on Transect Introduction

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Full All phases shown in Fig. 2 displayed very good linear TAlk-Sal relationships, indicating an overall two end-member mixing scheme for each phase.However, such two end-member mixing was not spatially homogeneous in the upper waters off Oregon during the sampling period.The top waters at stations 26-32 on Transect 4 were imprinted by the CR plume with salinity around ∼ 30.0.During the transport from the mouth of the CR estuary, the plume water increasingly mixed with adjacent oceanic waters, largely feeding its pathway.However, the majority of DIC and nutrients in waters immediately below the buoyant layer, as well as in surface waters at station 33 and possibly at station 25, should originate from deep waters through coastal upwelling and/or vertical mixing.The influence of the CR plume still occurred but was diluted by other freshwater masses such as rainwater, suggesting a mixing scheme between the deep water of the eNP and a combined freshwater end-member (Park, 1966(Park, , 1968)).Such mixing was also applicable to the surface waters at stations 35-38 on Transect 5. On the other hand, the upper 200 m waters or the entire water column at stations 39-41 on Transect 5 should result from a simple two end-member mixing between the upwelling source water in the CC and the rainwater with zero solutes, establishing for them an apparent OceMar-type system.

∆DIC and ∆ NO 3 in the upper waters off Oregon
The defined mixing schemes enabled us to estimate the nonconservative portion of DIC (∆DIC) and nitrate (∆NO 3 ) in the upper waters off Oregon following Dai et al. (2013): The superscripts "cons" and "meas" in Eqs. ( 1) and ( 2 water at station 39 (Fig. 1).The X eff in Eq. ( 3) denotes the effective concentration of DIC or NO 3 sourced from the freshwater input to various zones off Oregon.Since rainwater was assumed to have no solute, both DIC eff and NO 3 eff would be zero for waters in the surface mixed layer of stations 39-41 on Transect 5. On the other hand, the estimation of X eff associated with the CR followed the method for the OceMar case study of the CS, which has a noticeable DIC eff from the combination of the Amazon River and the Orinoco River (Dai et al., 2013).Since bicarbonate dominates other CO 2 species and other alkalinity components, DIC concentrations in the main stream of the CR are numerically similar to TAlk, which are also around ∼ 1000 µmol kg −1 (Park et al., 1969a(Park et al., , 1970)).This value was taken as the DIC end-member of the CR.The NO 3 end-member value was selected as 15 µmol kg http://www.stccmop.org/datamart/observation_network/fixedstation?id=saturn05# anchor_5).Assuming that the biological consumption of DIC and NO 3 in the CR plume followed the Redfield ratio (Redfield et al., 1963), the DIC removal was estimated to be Introduction

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Full ∼ 100 µmol kg −1 (approximately 15 • 106/16), while NO 3 was rapidly consumed along the pathway of the CR plume and generally depleted in the area beyond the plume (Aguilar-Islas and Bruland, 2006;Lohan and Bruland, 2006).As a consequence, the complete DIC eff and NO 3 eff in the upper waters off Oregon from the CR would be ∼ 900 µmol kg −1 and ∼ 0 µmol kg −1 .
If the combined freshwater end-member was a mixture of the CR and the rainwater with zero solutes, the intercept values of 517.5±29.2 (Fig. 2a) and 677.4±32.2 (Fig. 2b) derived from the TAlk-Sal regression indicated that the CR fractions were ∼ 50 % and ∼ 65 % (approximately 500/1000 and 650/1000 by taking ∼ 1000 µmol kg −1 as the TAlk end-member value of the CR, Park et al., 1969b;Evans et al., 2013).The DIC eff from the freshwater input was thus estimated to be ∼ 450 µmol kg −1 (approximately 900 • 50 %) for waters immediately below the top buoyant layer at stations 27-32 and waters in the surface mixed layer at stations 25 and 33 on Transect 4, which was slightly lower than that of ∼ 585 µmol kg −1 (approximately 900 • 65 %) for waters in the surface mixed layer at stations 35-38 on Transect 5.The NO 3 eff in any combined freshwater end-member was zero.Note that numerous small rivers are distributed on the Oregon Coast, which might also have diluted the CR plume inducing the lower intercept of the TAlk-Sal regression observed on Transects 4 and 5 (Fig. 2).The average wintertime discharge from these Coast Range rivers is estimated to be ∼ 2570 m 3 s −1 (Wetz et al., 2006), which is more than an order of magnitude higher than that in the summer (Colbert and McManus, 2003;Sigleo and Frick, 2003).However, the CR discharge in May to June 2007 reached its summit of ∼ 15 000 m 3 s −1 (Evans et al., 2013), which should be approximately two orders of magnitude higher than the discharge of small rivers.This significant contrast would suggest that inputs from small rivers should be negligible compared to the CR on Transect 4 and station 41 on Transect 5; Fig. 1) was as high as ∼ 32.5 and ∼ 34.0, respectively, which would rule out the influence of small rivers.

Evaluating the CO 2 source/sink nature in the upper waters off Oregon
The coupling of DIC and NO 3 dynamics could be then examined based on the classic Redfield ratio of C : N = 106 : 16 = 6.6 (Redfield et al., 1963).Positive values of the difference between ∆DIC and 6.6∆NO 3 (∆DIC-6.6∆NO3 ) suggested a CO 2 source term since "excess ∆DIC" was removed by CO 2 degassing into the atmosphere.In contrast, negative ∆DIC-6.6∆NO 3 suggested that "deficient ∆DIC" was supplied via the atmospheric CO 2 input to the ocean representing a CO 2 sink.Such net CO 2 exchange between the seawater and the atmosphere was further quantified as the sea-air difference of pCO 2 (∆pCO 2 ) via the Revelle factor (RF), which is referred to as the fractional change in seawater CO 2 over that of DIC at a given temperature, salinity and alkalinity and indicates the ocean's sensitivity to an increase in atmospheric CO 2 (Revelle and Suess, 1957;Sundquist et al., 1979).Because pCO 2 and CO 2 are proportional to each other, the RF can be illustrated as The sea-air ∆pCO 2 (i.e., ∂pCO 2 ) is thus obtained by Sea-air Here pCO 2 and DIC are the atmospheric pCO 2 (given an initial balance of sea-air CO 2 exchange) and sea surface DIC, respectively, and ∂DIC equals ∆DIC-6.6∆NO 3 .
As shown in Fig. 3, the estimated ∆DIC-6.6∆NO 3 values and their corresponding sea-air ∆pCO 2 in the upper waters off Oregon were overall below zero, suggesting a significant CO 2 sink nature.Introduction

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Transect 4
On Transect 4 off Newport, the average value of ∆DIC-6.6∆NO 3 was −23±2 µmol kg −1 in waters immediately below the top buoyant layer at stations 27-32, which equaled the average value for the surface mixed layer at station 33 (Fig. 3a).Although located at different depths, the two water parcels experienced similar physical mixing and biogeochemical modifications inducing the same CO 2 signature.The former water mass should work as a CO 2 sink when in contact with the atmosphere before or after the passage of the episodic CR plume.The average sea-air ∆pCO 2 resulting from the combined deficient ∆DIC was −54 ± 4 µatm (Fig. 3a).Given the atmospheric pCO 2 of ∼ 390 µatm (Evans et al., 2011), the seawater pCO 2 in these regions was thus estimated to be 336 ± 4 µatm, which agreed rather well with the field measurements of 334 ± 13 µatm (the underway seawater pCO 2 data were not available online but alternatively calculated by applying TAlk and DIC data into the CO2SYS program, Lewis and Wallace, 1998).
The diagnosis approach was not applied to the top buoyant layer since the aged CR plume might have experienced complex mixing with various surrounding water masses during its transport, as indicated by the scatter TAlk-Sal relationship (Fig. 2a).However, the far-field CR plume is suggested to be a strong sink of atmospheric CO 2 due to earlier biological consumption (Evans et al., 2011), which was supported by the observed low pCO 2 of ∼ 220-300 µatm in the top buoyant layer on Transect 4. As a consequence, the CO 2 sink nature in the upper waters from the outer shelf (bottom depth of station 27 was ∼ 170 m) to the open basin off Newport, Oregon would primarily result from the higher utilization of nutrients relative to DIC based on their concurrent inputs from deep waters.The nonlocal high productivity in the CR plume could inject even lower pCO 2 but this effect would be transitory.
At the innermost station 25 on Transect 4, highly positive values of ∆DIC-6.6∆NO 3 and sea-air ∆pCO 2 were obtained for the surface mixed layer of this station, indicating a significant CO 2 source.However, the lowest pCO 2 value of ∼ 170 µatm was observed

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Full in these nearshore waters off Oregon.The poor correlation between TAlk and salinity at station 25 (Fig. 2a) might compromise the estimation, whereas the same method (Eqs.1-5) was successfully applied to other stations on Transect 4 with a distinct TAlk-Sal relationship (i.e., the second phase in Fig. 2a).Note that coastal upwelling clearly influenced the bottom water at station 25 as indicated by the comparable salinity and TAlk values to those in offshore 200 m waters.Instead of being fed by the upwelled deep water, the DIC and nutrients in the surface mixed layer might have originated from horizontal admixture of the surrounding waters.These waters possibly experienced intense diatom blooms due to the fact that the surface silicate concentrations at station 25 were almost zero, which led to the most undersaturated pCO 2 condition observed in the upper waters off Oregon.

Transect 5
On Transect 5 near the Oregon-California border, the average ∆DIC-6.6∆NO3 and sea-air ∆pCO 2 were estimated to be −20 ± 3 µmol kg −1 and −48 ± 8 µatm in the surface mixed layer of offshore stations 35-38 (Fig. 3b).Both values were comparable to those obtained from Transect 4, indicating a similar magnitude of the CO 2 sink term.
The estimated sea surface pCO 2 of 342 ± 8 µatm was consistent with the field measurements of 332 ± 12 µatm in this region.
The ∆DIC-6.6∆NO 3 and sea-air ∆pCO 2 in the surface mixed layer of stations 39-41, although still below zero, were obviously higher than those of stations 35-38 (Fig. 3b).Such an increase was expected since stations 39-41 were located in the area with the most intense upwelling, which brought CO 2 -rich deep waters to the nearshore surface (Feely et al., 2008).However, our estimation suggested a weaker CO 2 sink or close to being in equilibrium with the estimated sea surface pCO 2 of 367 ± 12 µatm, whereas the field measurements of ∼ 650-1000 µatm indicated that the coastal upwelling zone should be a very strong source of CO 2 to the atmosphere.
A uniform salinity of ∼ 34.0 through the entire water column was observed at stations 40 and 41 due to the outcrop of the upwelling source water at the surface of the inner 7401 Introduction

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Full shelf on Transect 5 (Feely et al., 2008).Although salinity in the surface mixed layer at station 39 was lower, around ∼ 33.4, the dilution effect of rainwater should be negligible.
After removing the rainwater from the mixing scheme and calculating ∆DIC and ∆NO 3 by directly subtracting the field observed value from the end-member value for the upwelling source water (Eqs.6 and 7; DIC ref and NO 3 ref were field measurements of ∼ 200 m water samples at station 39), the ∆DIC-6.6∆NO3 values were rapidly increased to above zero in the surface mixed layer at stations 39 and 40, while values at station 41 with a small increase were still overall below zero (Fig. 4a).Correspondingly, the estimated sea surface pCO 2 values were higher than the atmospheric CO 2 value at stations 39 and 40 while they were slightly lower than that at station 41.However, these values still largely fell below the field measurements of seawater pCO 2 , displaying shoreward increasing differences from ∼ 200 µatm to ∼ 700 µatm (Fig. 4b).
∆DIC = DIC ref − DIC meas ( 6) With or without taking rainwater into account, our diagnosis approach did not work in the nearshore with strong upwelling off Oregon, even though the mixing scheme of this region was in accordance with the OceMar concept.We contend that OceMar assumes a steady state with balanced DIC and nutrients via both physical mixing and biological alterations in comparable timescales.However, the continuous inputs from the coastal upwelling might have led to the accumulation of DIC and nutrients in the nearshore surface, which could not be timely consumed by the phytoplankton community, suggesting a possible nonsteady state., 2011).Minor biological responses during the intensified upwelling period were also observed in summer 2008, allowing highly oversaturated pCO 2 surface water to persist on the inner shelf off Oregon for even nearly two months (Evans et al., 2011).At this point, it is uncertain why there was such a prolonged delay from the phytoplankton community to the persistent source of upwelled DIC and nutrients.Note that under the condition of more prevailing upwelling-favorable wind as a predicted consequence of climate change (e.g., Snyder et al., 2003;Diffenbaugh et al., 2004), the nearshore off Oregon in the upwelling season might always be in a nonsteady state, since fewer periodic relaxation events or reversals would further decrease the chance for the biological response to be factored in.
In addition, the negligible biological consumption might involve large errors when calculating ∆.The portion of ∆DIC and ∆NO 3 at station 41 relative to the preformed values of the upwelling source water were only ∼ 0.5 % and ∼ 10 %, slightly higher than the measurement uncertainties.The portion of DIC and NO 3 consumption in the surface mixed layer at offshore stations on Transect 5 were, however, one order of magnitude higher (∼ 7 % and ∼ 90 %, respectively).This contrast might partially explain why the OceMar framework did not work when insignificant biological alterations occurred.Given the predominant control of physical mixing, we contend that the prediction of the CO 2 flux in the nearshore off Oregon with intensified upwelling could be simplified without considering DIC/nutrient consumption.In other words, surface CO 2 levels in this region were simply imprints of the upwelling source water (pCO 2 ∼ 1100 µatm at ∼ 150-200 m) with minor dilution by rainwater.

Concluding remarks
The semi-analytical diagnosis approach of mass balance that couples physical transport and biogeochemical alterations was well applied to CO 2 sink zones off Oregon extending from the outer shelf to the open basin.In these zones without significant influence of the CR plume, the source of DIC was largely from deep waters of the eNP and Introduction

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Full the ultimate CO 2 sink nature was determined by the higher nutrient consumption than DIC in the upper waters.On the other hand, the estimated CO 2 flux was opposite to field observations in the coastal upwelling zone along the Oregon coast, which behaved like a typical OceMar system in terms of its mixing process.This discrepancy was very likely due to minor biological responses during the intensified upwelling period, making our mass balance approach based on the coupled physical biogeochemistry invalid.It suggested that the applicability of the proposed semi-analytical diagnosis approach is limited to steady state systems with comparable timescales of water mass mixing and biogeochemical reactions.In such physical mixing prevailing regime, resolving the CO 2 fluxes could be simplified without considering biological consumption of DIC and nutrients.Further work is however needed to understand the carbon and nutrient dynamics as well as the timing between physics and biology associated with coastal upwelling.Introduction

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Full  et al., 1963).The solid line indicates the pCO 2 equilibrium between the seawater and the atmosphere.In (b), the open and semi-filled symbols denote the estimated sea surface pCO 2 from ∆DIC-6.6∆NO 3 on top of the mixing with and without rainwater, respectively.The filled symbols denote the field observed sea surface pCO 2 , which were obtained by applying TAlk and DIC data into the CO2SYS program (Lewis and Wallace, 1998).The solid line denotes the atmospheric pCO 2 of ∼ 390 µatm (Evans et al., 2011).
Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | difficult because of the dynamic nature of both upwelling circulation and the associated biogeochemistry.
Discussion Paper | Discussion Paper | Discussion Paper | flow pattern with offshore shifting of the coastal jet and development of northward flow inshore.Along the southern part of the Oregon coast between 42.0 • N and 43.0 • N, an enhancement of upwelling, jet separation and eddy formation are observed to be as-Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Screen / Esc Printer-friendly Version Interactive Discussion Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) denote conservative-mixing induced and field measured values.In Eq. (3), X represents DIC or NO 3 while Sal meas Discussion Paper | Discussion Paper | Discussion Paper | is the CTD measured salinity.Sal ref and X ref are the reference salinity and concentration of DIC or NO 3 for the deep water end-member, which are the averages of all ∼ 200 m samples from stations involved in each mixing scheme.Specifically, for waters immediately below the top buoyant layer at stations 27-32 and waters in the surface mixed layer at stations 25 and 33 on Transect 4, the deep water end-member values of the reference salinity and concentrations of DIC or NO 3 were the averages of ∼ 200 m samples from stations 28-33 (Fig. 1).On Transect 5, the preformed salinity, DIC and NO 3 values for waters in the surface mixed layer at stations 35-38 were the averages of ∼ 200 m samples of these stations.For the upper waters at stations 39-41 influenced by the intensified upwelling, the deep water end-member was selected as the ∼ 200 m −1 based on recent years' observations in May and July at station SATURN-05 established in the upstream CR (database of the Center for Coastal Margin Observation and Prediction; Discussion Paper | Discussion Paper | Discussion Paper | plume.In particular, inputs from small rivers are normally restricted to a narrow band near the coast, whereas the research domain of this study has extended to the open basin of the eNP.Even the surface salinity at the innermost stations (i.e., station 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Fassbender et al. (2011) estimate that the age of the surface mixed layer at nearshore stations on Transect 5 is only ∼ 0.2 days, during which the DIC and NO 3 consumption via organic carbon production was almost zero and CaCO 3 dissolution contributed a small fraction to the slightly elevated DIC in the upwelled waters.They further predict that the nearshore surface pCO 2 on Transect Discussion Paper | Discussion Paper | Discussion Paper | et al.
Discussion Paper | Discussion Paper | Discussion Paper |