Abstract:The metabolism of the Arctic Ocean is marked by extremely pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (net community production, gross primary production and community respiration) along three different seasons of the year, for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the … Show more
“…Finally, because the vast majority of measurements of planktonic metabolism reported to date were conducted using in vitro incubations in borosilicate glass bottles (i.e. (Duarte et al ., ; Vaquer‐Sunyer et al ., ; Williams et al ., ; Serret et al ., ; Tilstone et al ., ), our results suggest that NCP rates reported for the surface ocean are likely to be biased, underestimating or overestimating NCP depending on the metabolic status of the communities (autotrophic or heterotrophic, respectively) and UVB penetration. We recommend that in vitro incubations of surface communities are conducted in quartz bottles, therefore allowing penetration of the full spectrum of solar radiation.…”
Aim
Erosion of the stratospheric ozone layer together with oligotrophication of the subtropical ocean is leading to enhanced exposure to ultraviolet B (UVB) radiation in ocean surface waters. The impact of increased exposure to UVB on planktonic primary producers and heterotrophs is uncertain. Here we test the null hypothesis that net community production (NCP) of plankton communities in surface waters of the tropical and subtropical ocean is not affected by ambient UVB radiation and extend this test to the global ocean, including the polar oceans and the Mediterranean Sea using previous results.
Location
We conducted experiments with 131 surface communities sampled during a circumnavigation cruise along the tropical and subtropical ocean and combined these results with 89 previous reports encompassing the Atlantic, Pacific, Arctic and Southern Oceans and the Mediterranean Sea.
Methods
The use of quartz (transparent to UVB radiation) and borosilicate glass materials (opaque to most UVB) for incubations allowed us to compare NCP between communities where UVB is excluded and those receiving natural UVB radiation.
Results
We found that NCP varies when exposed to natural UVB radiation compared to those where UVB was removed. NCP of autotrophic communities tended to decrease under natural UVB radiation, whereas the NCP of heterotrophic communities tended to increase. However, these variations showed the opposite trend under higher levels of UVB radiation.
Main conclusions
Our results suggest that earlier estimates of NCP for surface communities, which were hitherto derived using materials blocking UVB radiation were biased, with the direction and magnitude of this bias depending on the metabolic status of the communities and the underwater penetration of UVB radiation.
“…Finally, because the vast majority of measurements of planktonic metabolism reported to date were conducted using in vitro incubations in borosilicate glass bottles (i.e. (Duarte et al ., ; Vaquer‐Sunyer et al ., ; Williams et al ., ; Serret et al ., ; Tilstone et al ., ), our results suggest that NCP rates reported for the surface ocean are likely to be biased, underestimating or overestimating NCP depending on the metabolic status of the communities (autotrophic or heterotrophic, respectively) and UVB penetration. We recommend that in vitro incubations of surface communities are conducted in quartz bottles, therefore allowing penetration of the full spectrum of solar radiation.…”
Aim
Erosion of the stratospheric ozone layer together with oligotrophication of the subtropical ocean is leading to enhanced exposure to ultraviolet B (UVB) radiation in ocean surface waters. The impact of increased exposure to UVB on planktonic primary producers and heterotrophs is uncertain. Here we test the null hypothesis that net community production (NCP) of plankton communities in surface waters of the tropical and subtropical ocean is not affected by ambient UVB radiation and extend this test to the global ocean, including the polar oceans and the Mediterranean Sea using previous results.
Location
We conducted experiments with 131 surface communities sampled during a circumnavigation cruise along the tropical and subtropical ocean and combined these results with 89 previous reports encompassing the Atlantic, Pacific, Arctic and Southern Oceans and the Mediterranean Sea.
Methods
The use of quartz (transparent to UVB radiation) and borosilicate glass materials (opaque to most UVB) for incubations allowed us to compare NCP between communities where UVB is excluded and those receiving natural UVB radiation.
Results
We found that NCP varies when exposed to natural UVB radiation compared to those where UVB was removed. NCP of autotrophic communities tended to decrease under natural UVB radiation, whereas the NCP of heterotrophic communities tended to increase. However, these variations showed the opposite trend under higher levels of UVB radiation.
Main conclusions
Our results suggest that earlier estimates of NCP for surface communities, which were hitherto derived using materials blocking UVB radiation were biased, with the direction and magnitude of this bias depending on the metabolic status of the communities and the underwater penetration of UVB radiation.
“…5). Hence, whereas reported NCP for plankton communities in the Arctic Ocean 11–15 are robust, previous estimates of gross primary production and respiration rates are underestimates. The reason for this is that the assumption, rejected by our experimental results, that R light equals R dark is particularly inadequate for the high Arctic, where plankton communities do not experience darkness within the photic zone during the 24 h photoperiods in spring and summer.Figure 5The relationship between NCP calculated as GPP 18 O - R dark * exp[−0.02 + 0.68 * Ln (R light)] and observed net community production (NCP) in the Svalbard region (black symbols) and in Young Sound (white symbols).…”
Plankton respiration rate is a major component of global CO2 production and is forecasted to increase rapidly in the Arctic with warming. Yet, existing assessments in the Arctic evaluated plankton respiration in the dark. Evidence that plankton respiration may be stimulated in the light is particularly relevant for the high Arctic where plankton communities experience continuous daylight in spring and summer. Here we demonstrate that plankton community respiration evaluated under the continuous daylight conditions present in situ, tends to be higher than that evaluated in the dark. The ratio between community respiration measured in the light (Rlight) and in the dark (Rdark) increased as the 2/3 power of Rlight so that the Rlight:Rdark ratio increased from an average value of 1.37 at the median Rlight measured here (3.62 µmol O2 L−1 d−1) to an average value of 17.56 at the highest Rlight measured here (15.8 µmol O2 L−1 d−1). The role of respiratory processes as a source of CO2 in the Arctic has, therefore, been underestimated and is far more important than previously believed, particularly in the late spring, with 24 h photoperiods, when community respiration rates are highest.
“…In particular, our results show that ambient UV‐B radiation levels enhance net community production relative to communities where UV‐B is excluded. This suggests that previous analysis have underestimated NCP in Arctic communities, as all measurements reported were derived using borosilicate bottles [e.g., Regaudie‐de‐Gioux and Duarte , ; Vaquer‐Sunyer et al ., ], which exclude UV‐B radiation. This underestimation is highest at high NCP rates, typically observed in the spring [ Vaquer‐Sunyer et al ., ], and corresponds to an underestimation, for surface waters, where this bias is highest of 26% (Figure ).…”
In this study we report the response of net community production (NCP) of plankton communities in the Arctic surface waters exposure to natural ultraviolet radiation (UVR) conditions. A possible bias in previous measurements performed using borosilicate glass bottles (opaque to most UVR) can underestimate NCP. Here we show that 77% of the sampled communities suffer, on average, 38.5% of net increase in NCP when exposed to natural UV-B condition, relative to values when UV-B radiation is excluded. UV-B tends to shift communities toward autotrophy, with the most autotrophic communities responding the strongest. This is likely explained by the inhibition of bacterial respiration during the continuous day period of the Arctic summer, corroborated by experiments where bacterial production influenced by UV-B directly affect NCP. Whereas Arctic warming is expected to lead to lower NCP, our results show that increased UV-B radiation may partially compensate this negative effect in surface waters.
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