scholarly journals Characterizing upper-ocean mixing and its effect on the spring phytoplankton bloom with in situ data

2015 ◽  
Vol 72 (6) ◽  
pp. 1961-1970 ◽  
Author(s):  
Sarah R. Brody ◽  
M. Susan Lozier
Keyword(s):  
Mixed Layer ◽  
Spring Bloom ◽  
Phytoplankton Bloom ◽  
Upper Ocean ◽  
Late Winter ◽  
Uniform Density ◽  
Spring Phytoplankton Bloom ◽  
In Situ Data ◽  
Active Mixing

Abstract Since publication, the Sverdrup hypothesis, that phytoplankton are uniformly distributed within the ocean mixed layer and bloom once the ocean warms and stratifies in spring, has been the conventional explanation of subpolar phytoplankton spring bloom initiation. Recent studies have sought to differentiate between the actively mixing section of the upper ocean and the uniform-density mixed layer, arguing, as Sverdrup implied, that decreases in active mixing drive the spring bloom. In this study, we use in situ data to investigate the characteristics and depth of active mixing in both buoyancy- and wind-driven regimes and explore the idea that the shift from buoyancy-driven to wind-driven mixing in the late winter or early spring creates the conditions necessary for blooms to begin. We identify the bloom initiation based on net rates of biomass accumulation and relate changes in the depth of active mixing to changes in biomass depth profiles. These analyses support the idea that decreases in the depth of active mixing, a result of the transition from buoyancy-driven to wind-driven mixing, control the timing of the spring bloom.

scholarly journals Upper ocean mixing controls the seasonality of planktonic foraminifer fluxes and associated strength of the carbonate pump in the oligotrophic North Atlantic

2014 ◽  
Vol 11 (8) ◽  
pp. 12223-12254 ◽  
Author(s):  
K. H. Salmon ◽  
P. Anand ◽  
P. F. Sexton ◽  
M. Conte
Keyword(s):  
Mixed Layer ◽  
North Atlantic ◽  
Community Dynamics ◽  
Phytoplankton Bloom ◽  
North Atlantic Ocean ◽  
Planktonic Foraminifera ◽  
Upper Ocean ◽  
Late Winter ◽  
Planktonic Foraminifer ◽  
Spring Phytoplankton Bloom

Abstract. Oligotrophic regions represent up to 75% of Earth's open-ocean environments, and are typically characterized by nutrient-limited upper-ocean mixed layers. They are thus areas of major importance in understanding the plankton community dynamics and biogeochemical fluxes. Here we present fluxes of total planktonic foraminifera and eleven planktonic foraminifer species from a bi-weekly sediment trap time series in the oligotrophic Sargasso Sea, subtropical western North Atlantic Ocean at 1500 m water depth, over two ∼2.5 year intervals, 1998–2000 and 2007–2010. Foraminifera flux was closely correlated with total mass flux and with carbonate and organic carbon fluxes. We show that the planktonic foraminifera flux increases approximately five-fold during the winter–spring, contributing up to ∼40% of the total carbonate flux, driven primarily by increased fluxes of deeper dwelling ("globorotaliid") species. Interannual variability in total foraminifera flux, and in particular fluxes of the deep dwelling Globorotalia truncatulinoides, Globorotalia hirsuta, Globorotalia inflata, were related to differences in seasonal mixed layer dynamics affecting the strength of the spring phytoplankton bloom and export flux, and by the passage of mesoscale eddies. The heavily calcified, dense carbonate tests of deeper dwelling species (3 times denser than surface dwellers) can contribute up to 90% of the foraminiferal-derived carbonate in this region during late winter-early spring, implying a high seasonality of the biological carbonate pump in oligotrophic oceanic regions. Our data suggest that climate cycles, such as the North Atlantic Oscillation, that modulate the depth of the mixed layer, intensity of nutrient upwelling and primary production could also modulate the strength of the biological carbonate pump in the oligotrophic North Atlantic.

scholarly journals A newly observed physical cause of the onset of the subsurface spring phytoplankton bloom in the southwestern East Sea/Sea of Japan

2014 ◽  
Vol 11 (5) ◽  
pp. 1319-1329 ◽  
Author(s):  
Y.-T. Son ◽  
K.-I. Chang ◽  
S.-T. Yoon ◽  
T. Rho ◽  
J. H. Kwak ◽  
...  
Keyword(s):  
Sea Of Japan ◽  
Mixed Layer ◽  
Spring Bloom ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
East Sea ◽  
Ulleung Basin ◽  
Intermediate Water ◽  
Spring Phytoplankton Bloom ◽  
Bloom Period

Abstract. An ocean buoy, UBIM (Ulleung Basin Integrated Mooring), deployed during the spring transition from February to May 2010 reveals for the first time highly resolved temporal variation of biochemical properties of the upper layer of the Ulleung Basin in the southwestern East Sea/Sea of Japan. The time-series measurement captured the onset of subsurface spring bloom at 30 m, and collocated temperature and current data gives an insight into a mechanism that triggers the onset of the spring bloom not documented so far. Low-frequency modulation of the mixed layer depth ranging from 10 m to 53 m during the entire mooring period is mainly determined by shoaling and deepening of isothermal depths depending on the placement of UBIM on the cold or warm side of the frontal jet. The occurrence of the spring bloom at 30 m is concomitant with the appearance of colder East Sea Intermediate Water at buoy UBIM, which results in subsurface cooling and shoaling of isotherms to the shallower depth levels during the bloom period than those that occurred during the pre-bloom period. Isolines of temperature-based NO3 are also shown to be uplifted during the bloom period. It is suggested that the springtime spreading of the East Sea Intermediate Water is one of the important factors that triggers the subsurface spring bloom below the mixed layer.

The Advent of the Spring Bloom in the Eastern Subarctic Pacific Ocean

1966 ◽  
Vol 23 (4) ◽  
pp. 539-546 ◽  
Author(s):  
T. R. Parsons ◽  
L. F. Giovando ◽  
R. J. LeBrasseur
Keyword(s):  
Pacific Ocean ◽  
Primary Production ◽  
Mixed Layer ◽  
Spring Bloom ◽  
Phytoplankton Bloom ◽  
Central Area ◽  
Critical Depth ◽  
Spring Phytoplankton Bloom ◽  
Subarctic Pacific ◽  
Subarctic Pacific Ocean

The spring phytoplankton bloom in the eastern subarctic Pacific Ocean was described from estimations of the critical depth and the depth of the mixed layer. The results suggested that the spring bloom begins during February in the area south of 45°N and east of 135°W. During March the bloom area advances in a northwesterly direction to 50°N at 125°W and 45°N at 135°W. A net increase in primary production is also possible during March near 55°N and 155°W. During April, the spring bloom is generally well established throughout the region except in a central area where suitable conditions are not firmly established until May. This description is supported by the distribution of copepods in the region during April.

scholarly journals Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom

2014 ◽  
Vol 112 (1) ◽  
pp. E15-E20 ◽  
Author(s):  
Michael J. Ellwood ◽  
David A. Hutchins ◽  
Maeve C. Lohan ◽  
Angela Milne ◽  
Philipp Nasemann ◽  
...  
Keyword(s):  
Stable Isotopes ◽  
Mixed Layer ◽  
Phytoplankton Bloom ◽  
Iron Bioavailability ◽  
Global Ocean ◽  
Minor Role ◽  
Surface Mixed Layer ◽  
Spring Phytoplankton Bloom ◽  
Dissolved Iron ◽  
Particulate Iron

The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.

scholarly journals Upper-Ocean Thermal Structure and the Western North Pacific Category 5 Typhoons. Part II: Dependence on Translation Speed

2009 ◽  
Vol 137 (11) ◽  
pp. 3744-3757 ◽  
Author(s):  
I-I. Lin ◽  
Iam-Fei Pun ◽  
Chun-Chieh Wu
Keyword(s):  
Mixed Layer ◽  
North Pacific ◽  
Western North Pacific ◽  
Thermal Structure ◽  
Subsurface Layer ◽  
Heat Content ◽  
Correlation Coefficients ◽  
Upper Ocean ◽  
Translation Speed

Abstract Using new in situ ocean subsurface observations from the Argo floats, best-track typhoon data from the U.S. Joint Typhoon Warning Center, an ocean mixed layer model, and other supporting datasets, this work systematically explores the interrelationships between translation speed, the ocean’s subsurface condition [characterized by the depth of the 26°C isotherm (D26) and upper-ocean heat content (UOHC)], a cyclone’s self-induced ocean cooling negative feedback, and air–sea enthalpy fluxes for the intensification of the western North Pacific category 5 typhoons. Based on a 10-yr analysis, it is found that for intensification to category 5, in addition to the warm sea surface temperature generally around 29°C, the required subsurface D26 and UOHC depend greatly on a cyclone’s translation speed. It is observed that even over a relatively shallow subsurface warm layer of D26 ∼ 60–70 m and UOHC ∼ 65–70 kJ cm−2, it is still possible to have a sufficient enthalpy flux to intensify the storm to category 5, provided that the storm can be fast moving (typically Uh ∼ 7–8 m s−1). On the contrary, a much deeper subsurface layer is needed for slow-moving typhoons. For example at Uh ∼ 2–3 m s−1, D26 and UOHC are typically ∼115–140 m and ∼115–125 kJ cm−2, respectively. A new concept named the affordable minimum translation speed Uh_min is proposed. This is the minimum required speed a storm needs to travel for its intensification to category 5, given the observed D26 and UOHC. Using more than 3000 Argo in situ profiles, a series of mixed layer numerical experiments are conducted to quantify the relationship between D26, UOHC, and Uh_min. Clear negative linear relationships with correlation coefficients R = −0.87 (−0.71) are obtained as Uh_min = −0.065 × D26 + 11.1, and Uh_min = −0.05 × UOHC + 9.4, respectively. These relationships can thus be used as a guide to predict the minimum speed a storm has to travel at for intensification to category 5, given the observed D26 and UOHC.

scholarly journals Interannual Variability of the Mixed Layer Winter Convection and Spice Injection in the Eastern Subtropical North Atlantic

2015 ◽  
Vol 45 (2) ◽  
pp. 504-525 ◽  
Author(s):  
Nicolas Kolodziejczyk ◽  
Gilles Reverdin ◽  
Alban Lazar
Keyword(s):  
Interannual Variability ◽  
Mixed Layer ◽  
North Atlantic ◽  
Mixed Layer Depth ◽  
Buoyancy Flux ◽  
Upper Ocean ◽  
Late Winter ◽  
Layer Depth ◽  
Ocean Layer ◽  
Bulk Model

AbstractThe Argo dataset is used to study the winter upper-ocean conditions in the northeastern subtropical (NEA) Atlantic during 2006–12. During late winter 2010, the mixed layer depth is abnormally shallow and a negative anomaly of density-compensated salinity, the so-called spiciness, is generated in the permanent pycnocline. This is primarily explained by unusual weak air–sea buoyancy flux during the late winter 2010, in contrast with the five other studied winters. Particularly deep mixed layers and strong spiciness anomalies are observed during late winter 2012. The 2010 winter conditions appear to be related to historically low North Atlantic Oscillation (NAO) and high tropical North Atlantic index (TNA). Interannual variability of the eastern subtropical mixed layer is further investigated using a simple 1D bulk model of mean temperature and salinity linear profiles, based on turbulent kinetic energy conservation in the upper-ocean layer, and forced only with seasonal air–sea buoyancy forcing corresponding to fall–winter 2006–12. It suggests that year-to-year variability of the winter convective mixing driven by atmospheric buoyancy flux is able to generate interannual variability of both late winter mixed layer depth and spiciness in a strongly compensated layer at the base of the mixed layer and in the permanent pycnocline.

Modelling the Initiation of Spring Phytoplankton Blooms: a Synthesis of Physical and Biological Interannual Variability off Southwest Nova Scotia, 1983–85

1989 ◽  
Vol 46 (S1) ◽  
pp. s183-s199 ◽  
Author(s):  
R. Ian Perry ◽  
Peter C. F. Hurley ◽  
Peter C. Smith ◽  
J. Anthony Koslow ◽  
Robert O. Fournier
Keyword(s):  
Nova Scotia ◽  
Mixed Layer ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Critical Value ◽  
Zooplankton Biomass ◽  
Phytoplankton Production ◽  
Spring Phytoplankton Bloom ◽  
Turbulent Dissipation ◽  
Differential Advection

Chlorophyll and nitrate data from monthly surveys off southwest Nova Scotia indicate the spring phytoplankton bloom began near the end of March of each year, occurring early (late) in 1984 (1983). The highest chlorophyll biomass(all months) was found in 1985. Using survey data, the Sverdrup hypothesis for the initiation of the bloom was tested by comparing the critical depth, Zcr, for net phytoplankton production to the observed mixed-layer depth, Zmix. Survey median Zcr/Zmix were consistently less than 1 until May, suggesting that observed blooms were initiated by events outside the specific survey periods. Results of a mixed-layer model incorporating surface heating, differential advection and turbulent dissipation by wind and tide showed reasonable agreement with observed mixed depths, and patterns of the mean (modelled) mixed-layer light intensity are significantly correlated with observed chlorophyll biomass. In 1983 and 1984, mean light intensities first exceeded the critical value for a bloom to occur in late March. In 1985, transient periods of stratification in mid-February and early March produced intensities greater than the critical value. These events, together with higher nitrate concentrations and lower Zooplankton biomass, appear to be responsible for the high chlorophyll biomass observed in 1985.

In Situ Data Biases and Recent Ocean Heat Content Variability*

2009 ◽  
Vol 26 (4) ◽  
pp. 846-852 ◽  
Author(s):  
Josh K. Willis ◽  
John M. Lyman ◽  
Gregory C. Johnson ◽  
John Gilson
Keyword(s):  
Heat Content ◽  
Ocean Heat Content ◽  
Rate Equations ◽  
Upper Ocean ◽  
Cold Bias ◽  
Sampling Errors ◽  
Upper Ocean Heat Content ◽  
Data Errors ◽  
In Situ Data

Abstract Two significant instrument biases have been identified in the in situ profile data used to estimate globally integrated upper-ocean heat content. A large cold bias was discovered in a small fraction of Argo floats along with a smaller but more prevalent warm bias in expendable bathythermograph (XBT) data. These biases appear to have caused the bulk of the upper-ocean cooling signal reported by Lyman et al. between 2003 and 2005. These systematic data errors are significantly larger than sampling errors in recent years and are the dominant sources of error in recent estimates of globally integrated upper-ocean heat content variability. The bias in the XBT data is found to be consistent with errors in the fall-rate equations, suggesting a physical explanation for that bias. With biased profiles discarded, no significant warming or cooling is observed in upper-ocean heat content between 2003 and 2006.

A synthesis of upper ocean geostrophic kinetic energy spectra from a global submesoscale permitting simulation

2021 ◽  
Author(s):  
Hemant Khatri ◽  
Stephen Griffies ◽  
Takaya Uchida ◽  
Han Wang ◽  
Dimitris Menemenlis
Keyword(s):  
Kinetic Energy ◽  
Mixed Layer ◽  
Seasonal Variability ◽  
Ocean Model ◽  
Global Ocean ◽  
Upper Ocean ◽  
Late Winter ◽  
Second Phase ◽  
Ocean Turbulence ◽  
Two Phases

<p>In the upper ocean, submesoscale turbulence shows seasonal variability and is pronounced in winter. We analyze geostrophic KE spectra in a submesoscale-permitting global ocean model to study the seasonal variability in the upper ocean turbulence. Submesoscale processes peak in winter and, consequently, geostrophic kinetic energy (KE) spectra tend to be relatively shallow in winter (<em>k</em><sup>-2</sup>) with steeper spectra in summer (<em>k</em><sup>-3</sup>). The roles of frontogenesis processes and mixed-layer instabilities in submesoscale turbulence and their effects on the evolution of KE spectra over an annual cycle are discussed. It is shown that this transition in KE spectral scaling has two phases. In the first phase (late autumn), KE spectra show a presence of two spectral regimes: <em>k</em><sup>-3</sup> scaling in mesoscales (100-300 km) and <em>k</em><sup>-2</sup> scaling in submesoscales (< 50 km), indicating the coexistence of QG, surface-QG, and frontal dynamics. In the second phase (late winter), mixed-layer instabilities convert available potential energy into KE, which cascades upscale leading to flattening of the KE spectra at larger scales, and <em>k</em><sup>-2</sup> power-law develops in mesoscales too.</p>

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