Modeling vertical exchange of heat, salt, and other dissolved substances in the Cariaco Basin

Samodurov, A. S.; Scranton, Mary I.; Astor, Yrene; Иванов, Л. И.; Chukharev, A. M.; Белокопытов, В. Н.; Globina, Lubov

doi:10.1016/j.dsr.2012.09.001

Cited by 6 publications

(22 citation statements)

References 25 publications

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“…Our diffusivity estimates are substantially higher than estimates from previous studies in Cariaco Basin, all of which assumed an exponent of p = 1 (Li et al, ; Samodurov et al, ; Scranton et al, ; Taylor et al, ). An exponent greater than 1 ( p ≈ 1.7) is strongly supported by our fitted model, as the value p = 1 results in a much lower goodness of fit (Figure S13).…”

Section: Resultscontrasting

confidence: 80%

“…6 in Oslofjord (Norway), and Lewis and Perkin () used the salt budget to estimate D in Agfardlikavsa Fjord (Greenland), revealing a power law dependence on N with an exponent p ≈ 1.2 (Gargett, ). In Cariaco Basin, analogous parameter estimates are lacking, and previous studies simply assumed an exponent of p = 1 (Ho et al, ; Li et al, ; Samodurov et al, ; Scranton et al, ; Taylor et al, , ). A value of p = 1 is also frequently assumed in other systems (Yakushev, ; Yakushev et al, ; Zopfi, Ferdelman, Jorgensen, Teske, & Thamdrup, ), although some studies instead assumed p = 2 (Fennel & Boss, ; Reed et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…Specifically, for any given choice of α and p , we numerically solved the diffusion equation:

\frac{\partial \overset{false^}{S}}{\partial t} = \frac{\partial}{\partial z} [D (t, z) \frac{\partial \overset{false^}{S}}{\partial z}] + \frac{1}{A (z)} \frac{\partial A}{\partial z} [D (t, z) \frac{\partial \overset{false^}{S}}{\partial z}],

where

\overset{S}{true}

is the predicted salinity, D is the diffusivity calculated using Equation (1), and A ( z ) is the lateral (cross‐sectional) area of the basin at depth z (Figure S1). The last term in Equation (2) accounts for geometric dilution effects due to variation of the basin area over depth (Samodurov et al, ). This model omits occasional lateral intrusions of Caribbean Sea water (Samodurov et al, ; Scranton et al, ); the accuracy of the model is assessed in retrospect.…”

Section: Resultsmentioning

confidence: 99%

“…The last term in Equation (2) accounts for geometric dilution effects due to variation of the basin area over depth (Samodurov et al, ). This model omits occasional lateral intrusions of Caribbean Sea water (Samodurov et al, ; Scranton et al, ); the accuracy of the model is assessed in retrospect. We considered the depth range 150–900 m and the period spanning years 2001–2014, with boundary conditions provided by measured salinities at 150 m and 900 m. This depth range was chosen because 150 m is the maximum depth of the sill separating Cariaco Basin from the open ocean (and above which non‐diffusive salt transport due to lateral currents is more pronounced), and because 900 m is the depth of the saddle that separates the west and east sub‐basins in Cariaco (Taylor et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…The choice of z a is in principle arbitrary, as long as D ( z a ) can be determined somehow. A similar approach was used previously by Samodurov et al () to estimate D in Cariaco Basin, using the anchor depth z a = 150 m, with an important difference: Samodurov et al estimated D ( z a ) using the buoyancy‐frequency‐based formula in Equation (1), with α based on other marine systems and assuming p = 1, whereas here we made no assumption about D ( z a ) and instead estimated D ( z a ) from the salinity data via least‐squares fitting (details in Appendix S1). We emphasize that this estimate is strictly speaking only valid if the true diffusivity D does not vary with time, and hence, it should only be used as a rough sanity check.…”

Section: Resultsmentioning

confidence: 99%

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Microbial metabolite fluxes in a model marine anoxic ecosystem

et al. 2019

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Permanently anoxic regions in the ocean are widespread and exhibit unique microbial metabolic activity exerting substantial influence on global elemental cycles and climate. Reconstructing microbial metabolic activity rates in these regions has been challenging, due to the technical difficulty of direct rate measurements. In Cariaco Basin, which is the largest permanently anoxic marine basin and an important model system for geobiology, long‐term monitoring has yielded time series for the concentrations of biologically important compounds; however, the underlying metabolite fluxes remain poorly quantified. Here, we present a computational approach for reconstructing vertical fluxes and in situ net production/consumption rates from chemical concentration data, based on a 1‐dimensional time‐dependent diffusive transport model that includes adaptive penalization of overfitting. We use this approach to estimate spatiotemporally resolved fluxes of oxygen, nitrate, hydrogen sulfide, ammonium, methane, and phosphate within the sub‐euphotic Cariaco Basin water column (depths 150–900 m, years 2001–2014) and to identify hotspots of microbial chemolithotrophic activity. Predictions of the fitted models are in excellent agreement with the data and substantially expand our knowledge of the geobiology in Cariaco Basin. In particular, we find that the diffusivity, and consequently fluxes of major reductants such as hydrogen sulfide, and methane, is about two orders of magnitude greater than previously estimated, thus resolving a long‐standing apparent conundrum between electron donor fluxes and measured dark carbon assimilation rates.

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Section: Resultscontrasting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

“…Specifically, for any given choice of α and p , we numerically solved the diffusion equation:

\frac{\partial \overset{false^}{S}}{\partial t} = \frac{\partial}{\partial z} [D (t, z) \frac{\partial \overset{false^}{S}}{\partial z}] + \frac{1}{A (z)} \frac{\partial A}{\partial z} [D (t, z) \frac{\partial \overset{false^}{S}}{\partial z}],

where

\overset{S}{true}

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Microbial metabolite fluxes in a model marine anoxic ecosystem

et al. 2019

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Spatial and seasonal variability of dissolved organic matter in the Cariaco Basin

et al. 2013

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[1] Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were measured monthly at the CARIACO Time Series station (10 30 0 N, 64 40 0 W) in the southeastern Caribbean Sea between 2005 and 2012. Marked seasonal variability in DOC concentrations was observed, with lower values (~66 mM) in the upper water column (<75 m) during the upwelling season (December-April) due to the injection of cool, DOC-impoverished Subtropical Underwater from the Caribbean Sea. During the rainy season (May-November) waters were stratified and upper layer DOC concentrations increased to~71 mM. Interannual variability in surface (1 m) concentrations of DOC was also observed in response to the variable strength in upwelling and stratification that the Cariaco Basin experienced. DON and DOP showed no such seasonality. At depths >350 m, DOC concentrations were 56 AE 4.7 mM, roughly 10 mM higher than those in the Caribbean Sea over the same depth range. DON and DOP showed similar vertical profiles to that of DOC, with higher concentrations (6.8 AE 1.2 mM N and 0.15 AE0.09 mM P) in the upper water column and invariant, lower concentrations at depth (4.8 AE 1.6 mM N and 0.10 AE 0.08 mM P). Wind-driven advection of surface DOC out of the Cariaco Basin was estimated to support a net export~15 Gmol C yr À1 into the Caribbean Sea; this rate is comparable to the flux of settling particulate organic carbon to depths >275 m within the basin.

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