Estimating diffusivity from the mixed layer heat and salt balances in the <scp>N</scp>orth <scp>P</scp>acific

Cronin, Meghan F.; Pelland, Noel A.; Emerson, Steven; Crawford, William R.

doi:10.1002/2015jc011010

Cited by 97 publications

(150 citation statements)

References 32 publications

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“…The time series of ocean mixed layer temperature tendency shows that it has a strong seasonality, with increasing SSTs (positive temperature tendency) from approximately February to September each year and decreasing SSTs (negative temperature tendency) from October to January (Figure a). This temperature tendency is largely driven by the seasonality in net heat flux, which warms SSTs in the summer when insolation is highest and cools SSTs in the winter when turbulent heat fluxes dominate (Cronin et al, ). Horizontal advection contributes a positive temperature tendency by advecting warmer water from the western Pacific and from lower latitudes.…”

Section: Resultsmentioning

confidence: 99%

“…A mixed layer heat budget was constructed to analyze the processes contributing to anomalous SSTs during the NE Pacific MHW. Following Cronin et al (), the mixed layer temperature tendency is computed from the following equation:

\frac{\partial}{\partial t} T = \frac{Q_{o}}{ρ C_{p} h} - u_{a} \cdot \nabla T - ((), w_{h} + \frac{dh}{dt}) \frac{((), T - T_{h})}{h} - \frac{κ}{h} {\frac{\partial T}{\partial z}|}_{z = h}

where T is SST, Q o is net heat flux at the ocean surface, ρ C p is the volumetric heat capacity of water ( ρ C p = 4.088 × 10 6 J° · C −1 · m −3 ), h is the mixed layer depth, u a is ocean current velocity, w h is vertical velocity, T h is the temperature at the bottom of the mixed layer, κ is the diffusivity constant, and z is depth. The first term on the right side of the equation represents the contribution of ocean surface net heat flux to mixed layer temperature tendency, the second term represents the contribution by horizontal advection, the third term represents entrainment at the bottom of the mixed layer, and the fourth term represents vertical diffusivity at the bottom of the mixed layer.…”

Section: Methodsmentioning

confidence: 99%

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The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

et al. 2019

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Starting in late 2013, the Northeast (NE) Pacific Ocean experienced anomalously warm sea surface temperatures (SSTs) that persisted for over 2 years. This marine heatwave, known as “the Blob,” produced many devastating ecological impacts with socioeconomic implications for coastal communities. The warm waters observed during the NE Pacific 2013/2016 marine heatwave altered the surface energy balance and disrupted ocean–atmosphere interactions in the region. In principle, ocean–atmosphere interactions following the formation of the marine heatwave could have perpetuated warm SSTs through a positive SST‐cloud feedback. The actual situation was more complicated. While reanalysis data show a decrease in boundary layer cloud fraction and an increase in downward shortwave radiative flux at the surface coincident with warm SSTs, this was accompanied by an increase in longwave radiative fluxes at the surface, as well as an increase in sensible and latent heat fluxes out of the ocean mixed layer. The result is a small negative net heat flux anomaly (compared to the anomalies of the individual terms contributing to the net heat flux). This provides new information about the midlatitude ocean–atmosphere system while it was in a perturbed state. More specifically, a mixed layer heat budget reveals that anomalies in both the atmospheric and oceanic processes offset each other such that the anomalously warm SSTs persisted for multiple years. The results show how the atmosphere–ocean system in the NE Pacific is able to maintain itself in an anomalous state for an extended period of time.

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Section: Resultsmentioning

confidence: 99%

\frac{\partial}{\partial t} T = \frac{Q_{o}}{ρ C_{p} h} - u_{a} \cdot \nabla T - ((), w_{h} + \frac{dh}{dt}) \frac{((), T - T_{h})}{h} - \frac{κ}{h} {\frac{\partial T}{\partial z}|}_{z = h}

Section: Methodsmentioning

confidence: 99%

The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

et al. 2019

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“…Finally, the turbulent fluxes in the upper ocean (final terms in equations and ) are estimated to be negligible. Following Cronin et al (), turbulent heat and salt fluxes can be approximated using diffusivity constants κ T and κ S as

\begin{array}{l} left & ρ C_{p} \overset{true¯}{w' T'} |_{z = h} = - κ_{T} \overset{true¯}{\frac{\partial T}{\partial z}} |_{z = h} \\ left & ρ C_{p} \overset{true¯}{w' S'} |_{z = h} = - κ_{S} \overset{true¯}{\frac{\partial S}{\partial z}} |_{z = h} \end{array} .

…”

Section: Resultsmentioning

confidence: 99%

“…The salt budget proposed in Cronin et al () is adapted for use here as

Δ S C = \underset{1 : evap . & precip}{\underset{︸}{Δ t ρ false(E - P false) S_{0}}} - \underset{2 : ice source / sink}{\underset{︸}{ρ_{i c e} S_{i c e} Δ i c e_{o b s}}} - \underset{3 : horizontal advection}{\underset{︸}{Δ t ρ h \overset{u}{true} \cdot \nabla \overset{S}{true}}} - \underset{4 : turbulent flux}{\underset{︸}{Δ t ρ \overset{w' S'}{true} |_{z = h}}},

where term 1 represents evaporation and precipitation at the surface ( E and P ), with S 0 being the salinity at the surface. Term 2 is the change in salinity due to ice growth or melt and is based on the salinity of the ice ( S ice ) and the change in effective thickness of the ice ( ice obs ).…”

Section: Observational Methodsmentioning

confidence: 99%

Episodic Reversal of Autumn Ice Advance Caused by Release of Ocean Heat in the Beaufort Sea

et al. 2018

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High‐resolution measurements of the air‐ice‐ocean system during an October 2015 event in the Beaufort Sea demonstrate how stored ocean heat can be released to temporarily reverse seasonal ice advance. Strong on‐ice winds over a vast fetch caused mixing and release of heat from the upper ocean. This heat was sufficient to melt large areas of thin, newly formed pancake ice; an average of 10 MJ/m2 was lost from the upper ocean in the study area, resulting in ∼3–5 cm pancake sea ice melt. Heat and salt budgets create a consistent picture of the evolving air‐ice‐ocean system during this event, in both a fixed and ice‐following (Lagrangian) reference frame. The heat lost from the upper ocean is large compared with prior observations of ocean heat flux under thick, multiyear Arctic sea ice. In contrast to prior studies, where almost all heat lost goes into ice melt, a significant portion of the ocean heat released in this event goes directly to the atmosphere, while the remainder (∼30–40%) goes into melting sea ice. The magnitude of ocean mixing during this event may have been enhanced by large surface waves, reaching nearly 5 m at the peak, which are becoming increasingly common in the autumn Arctic Ocean. The wave effects are explored by comparing the air‐ice‐ocean evolution observed at short and long fetches, and a common scaling for Langmuir turbulence. After the event, the ocean mixed layer was deeper and cooler, and autumn ice formation resumed.

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“…Mixed layer velocity, used to estimate horizontal advection, is based upon current meter data from 5 m, 15 m, and 35 m, and a nearby upward looking Acoustic Doppler Current Profiler when available. Diffusivity at the base of the mixed layer was estimated by closing the mixed layer heat budget following Cronin et al []. The carbon budget, thus, relies upon nearly every measurement made on the mooring.…”

Section: Datamentioning

confidence: 99%

Net community production and calcification from 7 years of NOAA Station Papa Mooring measurements

Fassbender

Sabine

Cronin

2016

Global Biogeochemical Cycles

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104

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Seven years of near-continuous observations from the Ocean Station Papa (OSP) surface mooring were used to evaluate drivers of marine carbon cycling in the eastern subarctic Pacific. Processes contributing to mixed layer carbon inventory changes throughout each deployment year were quantitatively assessed using a time-dependent mass balance approach in which total alkalinity and dissolved inorganic carbon were used as tracers. By using two mixed layer carbon tracers, it was possible to isolate the influences of net community production (NCP) and calcification. Our results indicate that the annual NCP at OSP is 2 ± 1 mol C m À2 yr À1 and the annual calcification is 0.3 ± 0.3 mol C m À2 yr À1. Piecing together evidence for potentially significant dissolved organic carbon cycling in this region, we estimate a particulate inorganic carbon to particulate organic carbon ratio between 0.15 and 0.25. This is at least double the global average, adding to the growing evidence that calcifying organisms play an important role in carbon export at this location. These results, coupled with significant seasonality in the NCP, suggest that carbon cycling near OSP may be more complex than previously thought and highlight the importance of continuous observations for robust assessments of biogeochemical cycling.

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Estimating diffusivity from the mixed layer heat and salt balances in the North Pacific

Cited by 97 publications

References 32 publications

The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

Episodic Reversal of Autumn Ice Advance Caused by Release of Ocean Heat in the Beaufort Sea

Net community production and calcification from 7 years of NOAA Station Papa Mooring measurements

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