Seasonal mixed layer depth shapes phytoplankton physiology, viral production, and accumulation in the North Atlantic

AbstractSeasonal shifts in phytoplankton accumulation and loss largely follow changes in mixed layer depth, but the impact of mixed layer depth on cell physiology remains unexplored. Here, we investigate the physiological state of phytoplankton populations associated with distinct bloom phases and mixing regimes in the North Atlantic. Stratification and deep mixing alter community physiology and viral production, effectively shaping accumulation rates. Communities in relatively deep, early-spring mixed layers are characterized by low levels of stress and high accumulation rates, while those in the recently shallowed mixed layers in late-spring have high levels of oxidative stress. Prolonged stratification into early autumn manifests in negative accumulation rates, along with pronounced signatures of compromised membranes, death-related protease activity, virus production, nutrient drawdown, and lipid markers indicative of nutrient stress. Positive accumulation renews during mixed layer deepening with transition into winter, concomitant with enhanced nutrient supply and lessened viral pressure.

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Variability of the Oceanic Mixed Layer, 1960–2004

Journal of Climate ◽

10.1175/2007jcli1798.1 ◽

2008 ◽

Vol 21 (5) ◽

pp. 1029-1047 ◽

Cited By ~ 64

Author(s):

James A. Carton ◽

Semyon A. Grodsky ◽

Hailong Liu

Keyword(s):

Mixed Layer ◽

North Atlantic ◽

Southern Oscillation ◽

Mixed Layer Depth ◽

Global Ocean ◽

Boreal Summer ◽

Layer Depth ◽

The North ◽

The North Atlantic ◽

Mixed Layers

Abstract A new monthly uniformly gridded analysis of mixed layer properties based on the World Ocean Atlas 2005 global ocean dataset is used to examine interannual and longer changes in mixed layer properties during the 45-yr period 1960–2004. The analysis reveals substantial variability in the winter–spring depth of the mixed layer in the subtropics and midlatitudes. In the North Pacific an empirical orthogonal function analysis shows a pattern of mixed layer depth variability peaking in the central subtropics. This pattern occurs coincident with intensification of local surface winds and may be responsible for the SST changes associated with the Pacific decadal oscillation. Years with deep winter–spring mixed layers coincide with years in which winter–spring SST is low. In the North Atlantic a pattern of winter–spring mixed layer depth variability occurs that is not so obviously connected to local changes in winds or SST, suggesting that other processes such as advection are more important. Interestingly, at decadal periods the winter–spring mixed layers of both basins show trends, deepening by 10–40 m over the 45-yr period of this analysis. The long-term mixed layer deepening is even stronger (50–100 m) in the North Atlantic subpolar gyre. At tropical latitudes the boreal winter mixed layer varies in phase with the Southern Oscillation index, deepening in the eastern Pacific and shallowing in the western Pacific and eastern Indian Oceans during El Niños. In boreal summer the mixed layer in the Arabian Sea region of the western Indian Ocean varies in response to changes in the strength of the southwest monsoon.

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Organic nutrients as sources of N and P to the upper layers of the North Atlantic subtropical gyre along 24.5° N

Biogeosciences Discussions ◽

10.5194/bgd-7-4001-2010 ◽

2010 ◽

Vol 7 (3) ◽

pp. 4001-4044

Author(s):

A. Landolfi ◽

H. Dietze ◽

W. Koeve ◽

R. Mather ◽

R. Sanders

Keyword(s):

Mixed Layer ◽

North Atlantic ◽

N2 Fixation ◽

Mixed Layer Depth ◽

Subtropical Gyre ◽

Surface Mixed Layer ◽

Layer Depth ◽

The North ◽

Nutrient Utilisation ◽

The North Atlantic

Abstract. There is a longstanding discussion on how the macronutrient requirement of the export production in the North Atlantic subtropical gyre is sustained. In this study we asses the role of dissolved organic nitrogen (DON) and phosphorous (DOP) as sources of new nutrients into the North Atlantic subtropical gyre at 24.5° N. We define, based on measurements of DON, DOP, phytoplankton community structure, stable nitrogen isotopic signals, surface mixed layer depth and ocean color as viewed from space, four regions characterized by different nutrient supply regimes. Within these regions, two distinct loci of N2 fixation occur associated with different plankton assemblages and separated by a region in which N2 fixation occurs at levels insufficient to leave its distinctive isotopic fingerprint on the isotopic composition of PON. Here, the phosphorus supply pathways to the mixed plankton assemblage appear to be different. In the wester oligotrophic gyre (70–46° W), the lateral advection of DOP supplies the missing P that, together with, shallow mixed layer, almost permanent stratification and high water temperatures, stimulate diazotrophic growth, which augment TON local accumulation. In the eastern oligotophic gyre (46–30° W), DOP cannot support the P demand as it is exhausted on its way from productive areas. This is inferred from DOP turnover rates, estimated form enzymatic clevage rates, which are shorter (11 ± 8 months) than transit timescales, estimated from a 3-D circulation model (>4 yr). A stronger seasonal cycle in chlorophyll and mixed layer depth, favour some nutrient injections from below. Here additional N sources come from the advected DON which has a turnover-time of 6.7 ± 3 yr, instead fast remineralization and little DOP export are needed to maintain the P requirements. We conclude from these observations that organic nutrient utilisation patterns drive diverse phytoplankton assemblages and oceanic nitrogen fixation gradients.

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Satellite-Derived Ocean Thermal Structure for the North Atlantic Hurricane Season

Monthly Weather Review ◽

10.1175/mwr-d-15-0275.1 ◽

2016 ◽

Vol 144 (3) ◽

pp. 877-896 ◽

Cited By ~ 6

Author(s):

Iam-Fei Pun ◽

James F. Price ◽

Steven R. Jayne

Keyword(s):

Mixed Layer ◽

North Atlantic ◽

Thermal Structure ◽

Estimation Error ◽

Mixed Layer Depth ◽

Heat Content ◽

Height Anomaly ◽

The North ◽

Hurricane Season ◽

The North Atlantic

Abstract This paper describes a new model (method) called Satellite-derived North Atlantic Profiles (SNAP) that seeks to provide a high-resolution, near-real-time ocean thermal field to aid tropical cyclone (TC) forecasting. Using about 139 000 observed temperature profiles, a spatially dependent regression model is developed for the North Atlantic Ocean during hurricane season. A new step introduced in this work is that the daily mixed layer depth is derived from the output of a one-dimensional Price–Weller–Pinkel ocean mixed layer model with time-dependent surface forcing. The accuracy of SNAP is assessed by comparison to 19 076 independent Argo profiles from the hurricane seasons of 2011 and 2013. The rms differences of the SNAP-estimated isotherm depths are found to be 10–25 m for upper thermocline isotherms (29°–19°C), 35–55 m for middle isotherms (18°–7°C), and 60–100 m for lower isotherms (6°–4°C). The primary error sources include uncertainty of sea surface height anomaly (SSHA), high-frequency fluctuations of isotherm depths, salinity effects, and the barotropic component of SSHA. These account for roughly 29%, 25%, 19%, and 10% of the estimation error, respectively. The rms differences of TC-related ocean parameters, upper-ocean heat content, and averaged temperature of the upper 100 m, are ~10 kJ cm−2 and ~0.8°C, respectively, over the North Atlantic basin. These errors are typical also of the open ocean underlying the majority of TC tracks. Errors are somewhat larger over regions of greatest mesoscale variability (i.e., the Gulf Stream and the Loop Current within the Gulf of Mexico).

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AMOC hysteresis in an eddy-permitting GCM and monitoring indicators

10.5194/egusphere-egu2020-5498 ◽

2020 ◽

Author(s):

Laura Jackson ◽

Richard Wood

Keyword(s):

North Atlantic ◽

Large Scale ◽

Mixed Layer Depth ◽

Labrador Sea ◽

Layer Depth ◽

Weak State ◽

The North ◽

Vertical Density ◽

The North Atlantic ◽

Original Strength

<p>We conduct idealised experiments with HadGEM3-GC2, which is a pre-CMIP6 eddy-permitting GCM, to test for the presence of thresholds in the AMOC. We add fresh water to the North Atlantic for different rates and lengths of time, and then examine the AMOC recovery. In some cases the AMOC recovers to its original strength, however if the AMOC weakens sufficiently it does not recover and stays in a weak state for up to 300 years.</p><p>We test various indictors that have been proposed for monitoring the AMOC with this ensemble of experiments (and other scenarios). In particular we ask whether fingerprints can provide early warning or faster detection of weakening or recovery, or indications of crossing the threshold. We find metrics that perform best are the temperature metrics based on large scale differences, the large scale meridional density gradient, and the vertical density difference in the Labrador Sea. Mixed layer depth is also useful for indicating whether the AMOC recovers after weakening.&#160;</p>

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Mixed layer depth variability in the Red Sea

Ocean Science ◽

10.5194/os-14-563-2018 ◽

2018 ◽

Vol 14 (4) ◽

pp. 563-573 ◽

Cited By ~ 3

Author(s):

Cheriyeri P. Abdulla ◽

Mohammed A. Alsaafani ◽

Turki M. Alraddadi ◽

Alaa M. Albarakati

Keyword(s):

Red Sea ◽

Mixed Layer ◽

Mixed Layer Depth ◽

General Pattern ◽

Layer Depth ◽

Ocean Eddies ◽

The North ◽

Gap Winds ◽

Mixed Layers ◽

First Time

Abstract. For the first time, a monthly climatology of mixed layer depth (MLD) in the Red Sea has been derived based on temperature profiles. The general pattern of MLD variability is clearly visible in the Red Sea, with deep MLDs during winter and shallow MLDs during summer. Transitional MLDs have been found during the spring and fall. The northern end of the Red Sea experienced deeper mixing and a higher MLD associated with the winter cooling of the high-saline surface waters. Further, the region north of 19° N experienced deep mixed layers, regardless of the season. Wind stress plays a major role in the MLD variability of the southern Red Sea, while net heat flux and evaporation are the dominating factors in the central and northern Red Sea regions. Ocean eddies and Tokar Gap winds significantly alter the MLD structure in the Red Sea. The dynamics associated with the Tokar Gap winds leads to a difference of more than 20 m in the average MLD between the north and south of the Tokar axis.

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Estimating mixed layer nitrate in the North Atlantic Ocean

Biogeosciences ◽

10.5194/bg-7-795-2010 ◽

2010 ◽

Vol 7 (3) ◽

pp. 795-807 ◽

Cited By ~ 28

Author(s):

T. Steinhoff ◽

T. Friedrich ◽

S. E. Hartman ◽

A. Oschlies ◽

D. W. R. Wallace ◽

...

Keyword(s):

Neural Network ◽

Atlantic Ocean ◽

Observational Data ◽

Mixed Layer ◽

North Atlantic ◽

North Atlantic Ocean ◽

Mixed Layer Depth ◽

Model Data ◽

The North ◽

The North Atlantic

Abstract. Here we present an equation for the estimation of nitrate in surface waters of the North Atlantic Ocean (40° N to 52° N, 10° W to 60° W). The equation was derived by multiple linear regression (MLR) from nitrate, sea surface temperature (SST) observational data and model mixed layer depth (MLD) data. The observational data were taken from merchant vessels that have crossed the North Atlantic on a regular basis in 2002/2003 and from 2005 to the present. It is important to find a robust and realistic estimate of MLD because the deepening of the mixed layer is crucial for nitrate supply to the surface. We compared model data from two models (FOAM and Mercator) with MLD derived from float data (using various criteria). The Mercator model gives a MLD estimate that is close to the MLD derived from floats. MLR was established using SST, MLD from Mercator, time and latitude as predictors. Additionally a neural network was trained with the same dataset and the results were validated against both model data as a "ground truth" and an independent observational dataset. This validation produced RMS errors of the same order for MLR and the neural network approach. We conclude that it is possible to estimate nitrate concentrations with an uncertainty of ±1.4 μmol L−1 in the North Atlantic.

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Estimating mixed layer nitrate in the North Atlantic Ocean

Biogeosciences Discussions ◽

10.5194/bgd-6-8851-2009 ◽

2009 ◽

Vol 6 (5) ◽

pp. 8851-8881

Author(s):

T. Steinhoff ◽

T. Friedrich ◽

S. E. Hartman ◽

A. Oschlies ◽

D. W. R. Wallace ◽

...

Keyword(s):

Neural Network ◽

Atlantic Ocean ◽

Observational Data ◽

Mixed Layer ◽

North Atlantic ◽

North Atlantic Ocean ◽

Mixed Layer Depth ◽

Model Data ◽

The North ◽

The North Atlantic

Abstract. Here we present an equation for the estimation of nitrate in surface waters of the North Atlantic Ocean (40° N to 52° N, 10° W to 60° W). The equation was derived by multiple linear regression (MLR) from nitrate, sea surface temperature (SST) observational data and model mixed layer depth (MLD) data. The observational data were taken from merchant vessels that have crossed the North Atlantic on a regular basis in 2002/2003 and from 2005 to present. It is important to find a robust and realistic esitmate of MLD because the deepening of the mixed layer is crucial for nitrate supply to the surface. We compared model data from two models (FOAM and Mercator) with MLD derived from float data (using various criteria). The Mercator model gives a MLD estimate that is close to the MLD derived from floats. MLR was established using SST, MLD from Mercator, time and latitude as predictors. Additionally a neural network was trained with the same dataset and the results were validated against both model data as a "ground truth" and an independent observational dataset. This validation produced RMS errors of the same order for MLR and the neural network approach. We conclude that it is possible to estimate nitrate concentrations with an uncertainty of ±1.5 μmol L−1 in the North Atlantic.

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Mixed layer depth variability in the Red Sea

10.5194/os-2018-6 ◽

2018 ◽

Cited By ~ 1

Author(s):

Cheriyeri P. Abdulla ◽

Mohammed A. Alsaafani ◽

Turki M. Alraddadi ◽

Alaa M. Albarakati

Keyword(s):

Red Sea ◽

Mixed Layer ◽

Mixed Layer Depth ◽

General Pattern ◽

Layer Depth ◽

Ocean Eddies ◽

The North ◽

Gap Winds ◽

Mixed Layers ◽

First Time

Abstract. For the first time, a monthly climatology of mixed layer depth (MLD) in the Red Sea has been derived based on temperature profiles. The general pattern of MLD variability is clearly visible in the Red Sea, with deep MLDs during winter and shallow MLDs during summer. Transitional MLDs have been found during the spring and fall. The northern end of the Red Sea experienced deeper mixing and higher MLD, associated with the winter cooling of the high-saline surface waters. Further, the region north of 19° N experienced deep mixed layers, irrespective of the season. Wind stress plays a major role in the MLD variability of the southern Red Sea, while net heat flux and evaporation are the dominating factors in the central and northern Red Sea regions. Ocean eddies and Tokar gap winds significantly alter the MLD structure in the Red Sea. The dynamics associated with the Tokar gap winds lead to a difference of more than 20 m in the average MLD between the north and south of the Tokar axis.

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Space-Time Sea Surface pCO2 Estimation in the North Atlantic Based on CatBoost

Remote Sensing ◽

10.3390/rs13142805 ◽

2021 ◽

Vol 13 (14) ◽

pp. 2805

Author(s):

Hongwei Sun ◽

Junyu He ◽

Yihui Chen ◽

Boyu Zhao

Keyword(s):

North Atlantic ◽

Function Analysis ◽

Biological Activities ◽

Mixed Layer Depth ◽

Sea Surface ◽

Coefficient Of Determination ◽

Mean Bias Error ◽

Bias Error ◽

The North ◽

The North Atlantic

Sea surface partial pressure of CO2 (pCO2) is a critical parameter in the quantification of air–sea CO2 flux, which plays an important role in calculating the global carbon budget and ocean acidification. In this study, we used chlorophyll-a concentration (Chla), sea surface temperature (SST), dissolved and particulate detrital matter absorption coefficient (Adg), the diffuse attenuation coefficient of downwelling irradiance at 490 nm (Kd) and mixed layer depth (MLD) as input data for retrieving the sea surface pCO2 in the North Atlantic based on a remote sensing empirical approach with the Categorical Boosting (CatBoost) algorithm. The results showed that the root mean square error (RMSE) is 8.25 μatm, the mean bias error (MAE) is 4.92 μatm and the coefficient of determination (R2) can reach 0.946 in the validation set. Subsequently, the proposed algorithm was applied to the sea surface pCO2 in the North Atlantic Ocean during 2003–2020. It can be found that the North Atlantic sea surface pCO2 has a clear trend with latitude variations and have strong seasonal changes. Furthermore, through variance analysis and EOF (empirical orthogonal function) analysis, the sea surface pCO2 in this area is mainly affected by sea temperature and salinity, while it can also be influenced by biological activities in some sub-regions.

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Estimates of wind power and radiative near-inertial internal wave flux

Ocean Dynamics ◽

10.1007/s10236-020-01388-y ◽

2020 ◽

Vol 70 (11) ◽

pp. 1357-1376

Author(s):

Georg S. Voelker ◽

Dirk Olbers ◽

Maren Walter ◽

Christian Mertens ◽

Paul G. Myers

Keyword(s):

Energy Transfer ◽

Internal Wave ◽

Wind Power ◽

Mixed Layer ◽

North Atlantic ◽

Mixed Layer Depth ◽

Deep Ocean ◽

Wave Radiation ◽

Buoyancy Frequency ◽

The North

Abstract Energy transfer mechanisms between the atmosphere and the deep ocean have been studied for many years. Their importance to the ocean’s energy balance and possible implications on mixing are widely accepted. The slab model by Pollard (Deep-Sea Res Oceanogr Abstr 17(4):795–812, 1970) is a well-established simulation of near-inertial motion and energy inferred through wind-ocean interaction. Such a model is set up with hourly wind forcing from the NCEP-CFSR reanalysis that allows computations up to high latitudes without loss of resonance. Augmenting the one-dimensional model with the horizontal divergence of the near-inertial current field leads to direct estimates of energy transfer spectra of internal wave radiation from the mixed layer base into the ocean interior. Calculations using this hybrid model are carried out for the North Atlantic during the years 1989 and 1996, which are associated with positive and negative North Atlantic Oscillation index, respectively. Results indicate a range of meridional regimes with distinct energy transfer ratios. These are interpreted in terms of the mixed layer depth, the buoyancy frequency at the mixed layer base, and the wind field structure. The average ratio of radiated energy fluxes from the mixed layer to near-inertial wind power for both years is approximately 12%. The dependence on the wind structure is supported by simulations of idealized wind stress fronts with variable width and translation speeds.

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