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Physiological responses of coccolithophores to abrupt exposure of naturally low pH deep seawater

Physiological responses of coccolithophores to abrupt exposure of naturally low pH deep seawater
Physiological responses of coccolithophores to abrupt exposure of naturally low pH deep seawater
Upwelling is the process by which deep, cold, relatively high-CO2, nutrient-rich seawater rises to the sunlit surface of the ocean. This seasonal process has fueled geoengineering initiatives to fertilize the surface ocean with deep seawater to enhance productivity and thus promote the drawdown of CO2. Coccolithophores, which inhabit many upwelling regions naturally ‘fertilized’ by deep seawater, have been investigated in the laboratory in the context of ocean acidification to determine the extent to which nutrients and CO2 impact their physiology, but few data exist in the field except from mesocosms. Here, we used the Porcupine Abyssal Plain (north Atlantic Ocean) Observatory to retrieve seawater from depths with elevated CO2 and nutrients, mimicking geoengineering approaches. We tested the effects of abrupt natural deep seawater fertilization on the physiology and biogeochemistry of two strains of Emiliania huxleyi of known physiology. None of the strains tested underwent cell divisions when incubated in waters obtained from <1,000 m (pH = 7.99–8.08; CO2 = 373–485 p.p.m; 1.5–12 μM nitrate). However, growth was promoted in both strains when cells were incubated in seawater from ~1,000 m (pH = 7.9; CO2 ~560 p.p.m.; 14–17 μM nitrate) and ~4,800 m (pH = 7.9; CO2 ~600 p.p.m.; 21 μM nitrate). Emiliania huxleyi strain CCMP 88E showed no differences in growth rate or in cellular content or production rates of particulate organic (POC) and inorganic (PIC) carbon and cellular particulate organic nitrogen (PON) between treatments using water from 1,000 m and 4,800 m. However, despite the N:P ratio of seawater being comparable in water from ~1,000 and ~4,800 m, the PON production rates were three times lower in one incubation using water from ~1,000 m compared to values observed in water from ~4,800 m. Thus, the POC:PON ratios were threefold higher in cells that were incubated in ~1,000 m seawater. The heavily calcified strain NZEH exhibited lower growth rates and PIC production rates when incubated in water from ~4,800 m compared to ~1,000 m, while cellular PIC, POC and PON were higher in water from 4,800 m. Calcite Sr/Ca ratios increased with depth despite constant seawater Sr/Ca, indicating that upwelling changes coccolith geochemistry. Our study provides the first experimental and field trial of a geoengineering approach to test how deep seawater impacts coccolithophore physiological and biogeochemical properties. Given that coccolithophore growth was only stimulated using waters obtained from >1,000 m, artificial upwelling using shallower waters may not be a suitable approach for promoting carbon sequestration for some locations and assemblages, and should therefore be investigated on a site-by-site basis.
1932-6203
Iglesias-rodriguez, Maria Debora
23b993ce-be9f-456c-a7d3-a3a4ad405586
Jones, Bethan, M.
2a40cabe-e5ee-4454-8aab-585c3af9fa70
Blanco-ameijeiras, Sonia
d6a71690-783f-4674-8b6c-1d3d20dc4497
Greaves, Mervyn
fad09383-f4cc-4b10-b04f-06699f7f6b95
Huete-ortega, Maria
5bc1f344-81f3-4be1-acb3-a7e9d55cab9d
Lebrato, Mario
0c14d20e-c641-4a61-8ba2-b6377cdf1777
Iglesias-rodriguez, Maria Debora
23b993ce-be9f-456c-a7d3-a3a4ad405586
Jones, Bethan, M.
2a40cabe-e5ee-4454-8aab-585c3af9fa70
Blanco-ameijeiras, Sonia
d6a71690-783f-4674-8b6c-1d3d20dc4497
Greaves, Mervyn
fad09383-f4cc-4b10-b04f-06699f7f6b95
Huete-ortega, Maria
5bc1f344-81f3-4be1-acb3-a7e9d55cab9d
Lebrato, Mario
0c14d20e-c641-4a61-8ba2-b6377cdf1777

Iglesias-rodriguez, Maria Debora, Jones, Bethan, M., Blanco-ameijeiras, Sonia, Greaves, Mervyn, Huete-ortega, Maria and Lebrato, Mario (2017) Physiological responses of coccolithophores to abrupt exposure of naturally low pH deep seawater. PLoS ONE, 12 (7). (doi:10.1371/journal.pone.0181713).

Record type: Article

Abstract

Upwelling is the process by which deep, cold, relatively high-CO2, nutrient-rich seawater rises to the sunlit surface of the ocean. This seasonal process has fueled geoengineering initiatives to fertilize the surface ocean with deep seawater to enhance productivity and thus promote the drawdown of CO2. Coccolithophores, which inhabit many upwelling regions naturally ‘fertilized’ by deep seawater, have been investigated in the laboratory in the context of ocean acidification to determine the extent to which nutrients and CO2 impact their physiology, but few data exist in the field except from mesocosms. Here, we used the Porcupine Abyssal Plain (north Atlantic Ocean) Observatory to retrieve seawater from depths with elevated CO2 and nutrients, mimicking geoengineering approaches. We tested the effects of abrupt natural deep seawater fertilization on the physiology and biogeochemistry of two strains of Emiliania huxleyi of known physiology. None of the strains tested underwent cell divisions when incubated in waters obtained from <1,000 m (pH = 7.99–8.08; CO2 = 373–485 p.p.m; 1.5–12 μM nitrate). However, growth was promoted in both strains when cells were incubated in seawater from ~1,000 m (pH = 7.9; CO2 ~560 p.p.m.; 14–17 μM nitrate) and ~4,800 m (pH = 7.9; CO2 ~600 p.p.m.; 21 μM nitrate). Emiliania huxleyi strain CCMP 88E showed no differences in growth rate or in cellular content or production rates of particulate organic (POC) and inorganic (PIC) carbon and cellular particulate organic nitrogen (PON) between treatments using water from 1,000 m and 4,800 m. However, despite the N:P ratio of seawater being comparable in water from ~1,000 and ~4,800 m, the PON production rates were three times lower in one incubation using water from ~1,000 m compared to values observed in water from ~4,800 m. Thus, the POC:PON ratios were threefold higher in cells that were incubated in ~1,000 m seawater. The heavily calcified strain NZEH exhibited lower growth rates and PIC production rates when incubated in water from ~4,800 m compared to ~1,000 m, while cellular PIC, POC and PON were higher in water from 4,800 m. Calcite Sr/Ca ratios increased with depth despite constant seawater Sr/Ca, indicating that upwelling changes coccolith geochemistry. Our study provides the first experimental and field trial of a geoengineering approach to test how deep seawater impacts coccolithophore physiological and biogeochemical properties. Given that coccolithophore growth was only stimulated using waters obtained from >1,000 m, artificial upwelling using shallower waters may not be a suitable approach for promoting carbon sequestration for some locations and assemblages, and should therefore be investigated on a site-by-site basis.

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Accepted/In Press date: 6 July 2017
e-pub ahead of print date: 27 July 2017

Identifiers

Local EPrints ID: 413296
URI: https://eprints.soton.ac.uk/id/eprint/413296
ISSN: 1932-6203
PURE UUID: 018e34f7-f4c2-4fc0-bd9b-ea04154ec8dd

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Date deposited: 21 Aug 2017 16:31
Last modified: 18 Nov 2019 18:42

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