Characterizing the subsurface chlorophyll a maximum in the Chukchi Sea and Canada Basin

Brown, Zachary W.; Lowry, Kate E.; Palmer, Molly A.; Dijken, Gert L. van; Mills, Matthew M.; Pickart, Robert S.; Arrigo, Kevin R.

doi:10.1016/j.dsr2.2015.02.010

Cited by 72 publications

(86 citation statements)

References 50 publications

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“…Under MW, the SCM was usually found at or below the nutricline (Figure h) indicating that SCM depth in CWW is determined by nutricline depth, consistent with other studies [ Brown et al ., ; Lowry et al ., ]. The relationship was not as clear where there was CSW, but the limited data suggest that the CSW SCM is more likely to be found above the nutricline (Figure g).…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies have shown that phytoplankton growth and SCM depth are correlated with the availability of light and the vertical structure of nutrient concentrations [ Martin et al ., ; McLaughlin and Carmack , ; Wassmann and Reigstad , ; Brown et al ., ; Coupel et al ., ; Lowry et al ., ]. On the Chukchi shelf, the nitracline is located between high nutrient concentrations in the deep WW and low nutrients in surface CSW and MW layers and affects SCM depth and biomass [ Brown et al ., ; Coupel et al ., ]. Nitrate usage in the Chukchi Sea likely has downstream effects in the Arctic, as Winter Water originating in the Chukchi Sea is an important source of nitrate to the deep Arctic basin [ Walsh et al ., ].…”

Section: Introductionmentioning

confidence: 99%

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Dependence of subsurface chlorophyll on seasonal water masses in the Chukchi Sea

et al. 2016

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During the late summer, phytoplankton in the northeastern Chukchi Sea are typically found in subsurface layers. These layers and their sensitivity to local changes in hydrography and nutrient concentrations are characterized by combining data from a high‐resolution towed sampling platform with traditional shipboard observations. The replacement of surface meltwater and deeper nutrient‐rich Chukchi Winter Water by northward flowing nutrient‐poor Chukchi Summer Water and Remnant Winter Water leads to a net decrease in biomass and smaller phytoplankton. Between 17 and 67% of phytoplankton biomass is contained within the subsurface layers. This estimate is nearly twice as high as previous estimates from sparser shipboard data and suggests subsurface phytoplankton contribute significantly to the net biomass in the Chukchi Sea in late summer.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dependence of subsurface chlorophyll on seasonal water masses in the Chukchi Sea

et al. 2016

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“…In the Canada Basin, a subsurface chlorophyll a maximum generally develops at a depth of ~60 m, which corresponds to the deeper subsurface chlorophyll a maximum observed in the present study. This maximum has been well studied, including in terms of its distribution and seasonal dynamics (Brown et al, ; Carmack et al, ; Tremblay et al, ), biogeochemical significance (Martin et al, ), interannual changes in depth (McLaughlin & Carmack, ), and future projections (Steiner et al, ). However, the shallower subsurface chlorophyll a maximum at ~20 m has not been well studied to date.…”

Section: Discussionmentioning

confidence: 99%

Do Strong Winds Impact Water Mass, Nutrient, and Phytoplankton Distributions in the Ice‐Free Canada Basin in the Fall?

et al. 2020

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In general, strong wind events can enhance ocean turbulent mixing, followed by episodic nutrient supply to the euphotic zone and phytoplankton blooms. However, it is unclear whether such responses to strong winds occur in the ice-free Canada Basin, where the seasonal pycnocline is strong and the nutricline is deep. In the present study, we monitored a fixed-point observation (FPO) station in the Canada Basin for about 3 weeks in the fall of 2014 to examine the oceanic and biological responses to strong winds. At the FPO site, oceanic microstructure measurements, hydrographic surveys, and water sampling were performed with high temporal resolution, recording internal wave propagation, eddy passage, and water mass changes. Strong winds and internal wave propagation significantly enhanced the mixing above and at the seasonal pycnocline, but their effects were diminished at the nutricline, which was much deeper than the seasonal pycnocline. Therefore, wind-induced mixing did not increase the upward nutrient supply from the nutricline and did not impact phytoplankton (chlorophyll a) distribution in the surface layer of the FPO site. The temporal evolution of the chlorophyll a concentration was most closely related to water mass changes. We also observed prominent subsurface chlorophyll a maxima with abundant large-sized phytoplankton that were likely carried by warm-core eddies to the FPO site. Phytoplankton biomass may have been sustained by the high concentration of ammonium within the eddy and ammonium regeneration at the seasonal pycnocline, where particulate organic matter likely accumulated.Plain Language Summary The Arctic basins, once covered with multiyear ice, are gaining ice-free areas in summer and fall as an effect of global warming. An ice-free upper ocean is more susceptible to wind forcing than ice-covered waters. Here, we studied the oceanic and biological responses to strong winds in the ice-free Canada Basin, where a density gap (pycnocline) was seasonally formed at a depth of about 20 m between the sea surface layer containing sea ice meltwater and the layer below. Although significant wind-induced mixing was observed above and at this seasonal pycnocline, mixing was attenuated at nutricline depths (~60 m), where nutrient concentrations increased strongly with depth. Thus, nutrients were not supplied from the nutricline to the sea surface layer through wind-induced mixing, and phytoplankton biomass did not increase in response to strong winds. However, phytoplankton biomass sometimes increased around the seasonal pycnocline, where ammonium was available for use in photosynthesis. This ammonium was likely supplied by warm-core eddies transporting shelf water into the Canada Basin. Another conceivable source of ammonium was particulate organic matter suspended at the seasonal pycnocline that decomposed, producing ammonium.

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“…The bottom waters in the Chukchi Sea that originate from the Pacific Ocean in summer and winter are characterised by T and S. In summer, they can be classified into three water masses: Anadyr water (S > 32.5, T = −1.0-1.5 • C) in the west, Bering shelf water (S = 31.8-32.5, T = 0-4 • C) in the centre, and Alaskan coastal water (ACW; S < 31.8, T > 4 • C) near the Alaskan coast (Coachman et al, 1975;Coachman, 1987;Grebmeier et al, 1988). As the Anadyr and Bering shelf waters are usually not distinct in the Chukchi Sea, the combined water mass is called the Bering shelf-Anadyr water (BSAW; S ≥ 31.8, T = −1.0-4 • C).…”

Section: Mooring Datamentioning

confidence: 99%

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

et al. 2016

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Characterizing the subsurface chlorophyll a maximum in the Chukchi Sea and Canada Basin

Cited by 72 publications

References 50 publications

Dependence of subsurface chlorophyll on seasonal water masses in the Chukchi Sea

Dependence of subsurface chlorophyll on seasonal water masses in the Chukchi Sea

Do Strong Winds Impact Water Mass, Nutrient, and Phytoplankton Distributions in the Ice‐Free Canada Basin in the Fall?

Water mass characteristics and their temporal changes in a biological hotspot in the southern Chukchi Sea

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