Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific
The offshore Gulf of Alaska—in the northeastern subarctic Pacific—is a high-nitrate, low-chlorophyll (HNLC) oceanic region where concentrations of dissolved iron (DFe) and zinc (DZn) are of the order ~0.1 nmol kg−1 in surface waters. At the average winter mixed layer depth of ~120 m, DFe and DZn are...
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Frontiers Media S.A.
2022-09-01
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| Series: | Frontiers in Marine Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fmars.2022.933823/full |
| _version_ | 1798031819221762048 |
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| author | David W. Crawford Duncan A. Purdie Maeve C. Lohan Peter J. Statham Tawnya D. Peterson Hilary A. Kennedy Michael S. Lipsen Jennifer N. Putland Frank A. Whitney |
| author_facet | David W. Crawford Duncan A. Purdie Maeve C. Lohan Peter J. Statham Tawnya D. Peterson Hilary A. Kennedy Michael S. Lipsen Jennifer N. Putland Frank A. Whitney |
| author_sort | David W. Crawford |
| collection | DOAJ |
| description | The offshore Gulf of Alaska—in the northeastern subarctic Pacific—is a high-nitrate, low-chlorophyll (HNLC) oceanic region where concentrations of dissolved iron (DFe) and zinc (DZn) are of the order ~0.1 nmol kg−1 in surface waters. At the average winter mixed layer depth of ~120 m, DFe and DZn are of the orders ~0.1–0.2 nmol kg−1 and ~1–2 nmol kg−1, respectively. Vertical supply of Fe to surface waters is therefore limited, with phytoplankton blooms driven by episodic atmospheric and lateral inputs of Fe. In contrast, DZn is presumably replenished through seasonal vertical mixing, though maintained at low levels in surface waters, even in winter, implying that removal processes are in operation. Previous supplementation experiments have demonstrated that phytoplankton biomass (chl-a), growth, and drawdown of nitrate (NO3-) are stimulated strongly by Fe but only minimally, if at all, by Zn alone. Using on-deck bioassay incubations of surface waters, we confirm that the addition of Fe stimulates significant increases in chl-a and large diatoms, and drawdown of NO3- and silicic acid [Si(OH)4]. Associated drawdown of DZn and dissolved cadmium (DCd) indicated Zn stress in the control and +Fe treatment. Supplementation with Zn alone had no significant impact on NO3- and commonly monitored pigments such as chl-a and fucoxanthin. However, in the +Zn treatment, DFe and coccolithophore abundance were significantly lower, and the concentration of particulate organic carbon (POC) and that of the pigments alloxanthin and chlorophyll c1+2 were significantly higher than those in control incubations. Our experiment corroborates previously observed relationships between DZn and alloxanthin and chlorophyll c across the subarctic north Pacific and Bering Sea and could help to explain the low or undetectable concentrations of alloxanthin frequently observed in this region. Alloxanthin is a pigment specific to the cryptophytes, either within free-living cells or within functional plastids retained by mixotrophic protists. Both cryptophytes and mixotrophic ciliates, such as Laboea sp. and Strombidium spp., make a variable but significant contribution to phytoplankton biomass in this area. In the absence of Fe supply to surface waters, Zn could play a hitherto unsuspected role in shaping plankton communities in the HNLC Gulf of Alaska. |
| first_indexed | 2024-04-11T20:02:39Z |
| format | Article |
| id | doaj.art-91b0db18b77342e3b59e426e3f32356d |
| institution | Directory Open Access Journal |
| issn | 2296-7745 |
| language | English |
| last_indexed | 2024-04-11T20:02:39Z |
| publishDate | 2022-09-01 |
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| spelling | doaj.art-91b0db18b77342e3b59e426e3f32356d2022-12-22T04:05:31ZengFrontiers Media S.A.Frontiers in Marine Science2296-77452022-09-01910.3389/fmars.2022.933823933823Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic PacificDavid W. Crawford0Duncan A. Purdie1Maeve C. Lohan2Peter J. Statham3Tawnya D. Peterson4Hilary A. Kennedy5Michael S. Lipsen6Jennifer N. Putland7Frank A. Whitney8School of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United KingdomSchool of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United KingdomSchool of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United KingdomSchool of Ocean and Earth Science, National Oceanography Centre, University of Southampton, Southampton, United KingdomOregon Health & Science University, School of Public Health, Portland State University, Portland, OR, United StatesSchool of Ocean Sciences, Bangor University, Anglesey, United KingdomDepartment of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, BC, CanadaIndependent Researcher, Victoria, BC, CanadaCentre for Ocean Climate Chemistry, Institute of Ocean Sciences, Sidney, BC, CanadaThe offshore Gulf of Alaska—in the northeastern subarctic Pacific—is a high-nitrate, low-chlorophyll (HNLC) oceanic region where concentrations of dissolved iron (DFe) and zinc (DZn) are of the order ~0.1 nmol kg−1 in surface waters. At the average winter mixed layer depth of ~120 m, DFe and DZn are of the orders ~0.1–0.2 nmol kg−1 and ~1–2 nmol kg−1, respectively. Vertical supply of Fe to surface waters is therefore limited, with phytoplankton blooms driven by episodic atmospheric and lateral inputs of Fe. In contrast, DZn is presumably replenished through seasonal vertical mixing, though maintained at low levels in surface waters, even in winter, implying that removal processes are in operation. Previous supplementation experiments have demonstrated that phytoplankton biomass (chl-a), growth, and drawdown of nitrate (NO3-) are stimulated strongly by Fe but only minimally, if at all, by Zn alone. Using on-deck bioassay incubations of surface waters, we confirm that the addition of Fe stimulates significant increases in chl-a and large diatoms, and drawdown of NO3- and silicic acid [Si(OH)4]. Associated drawdown of DZn and dissolved cadmium (DCd) indicated Zn stress in the control and +Fe treatment. Supplementation with Zn alone had no significant impact on NO3- and commonly monitored pigments such as chl-a and fucoxanthin. However, in the +Zn treatment, DFe and coccolithophore abundance were significantly lower, and the concentration of particulate organic carbon (POC) and that of the pigments alloxanthin and chlorophyll c1+2 were significantly higher than those in control incubations. Our experiment corroborates previously observed relationships between DZn and alloxanthin and chlorophyll c across the subarctic north Pacific and Bering Sea and could help to explain the low or undetectable concentrations of alloxanthin frequently observed in this region. Alloxanthin is a pigment specific to the cryptophytes, either within free-living cells or within functional plastids retained by mixotrophic protists. Both cryptophytes and mixotrophic ciliates, such as Laboea sp. and Strombidium spp., make a variable but significant contribution to phytoplankton biomass in this area. In the absence of Fe supply to surface waters, Zn could play a hitherto unsuspected role in shaping plankton communities in the HNLC Gulf of Alaska.https://www.frontiersin.org/articles/10.3389/fmars.2022.933823/fullNortheastern Subarctic Pacificphytoplanktoncryptophytesmixotrophic protiststrace metalszinc |
| spellingShingle | David W. Crawford Duncan A. Purdie Maeve C. Lohan Peter J. Statham Tawnya D. Peterson Hilary A. Kennedy Michael S. Lipsen Jennifer N. Putland Frank A. Whitney Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific Frontiers in Marine Science Northeastern Subarctic Pacific phytoplankton cryptophytes mixotrophic protists trace metals zinc |
| title | Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific |
| title_full | Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific |
| title_fullStr | Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific |
| title_full_unstemmed | Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific |
| title_short | Apparent shifts in the microplankton community in response to zinc and iron enrichments in the Northeastern Subarctic Pacific |
| title_sort | apparent shifts in the microplankton community in response to zinc and iron enrichments in the northeastern subarctic pacific |
| topic | Northeastern Subarctic Pacific phytoplankton cryptophytes mixotrophic protists trace metals zinc |
| url | https://www.frontiersin.org/articles/10.3389/fmars.2022.933823/full |
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