UV sensitivity of planktonic net community production in ocean surface waters

Abstract

The net plankton community metabolism of oceanic surface waters is particularly important as it more directly affects the partial pressure of CO 2 in surface waters and thus the air-sea fluxes of CO 2 . Plankton communities in surface waters are exposed to high irradiance that includes significant ultraviolet blue (UVB, 280-315 nm) radiation. UVB radiation affects both photosynthetic and respiration rates, increase plankton mortality rates, and other metabolic and chemical processes. Here we test the sensitivity of net community production (NCP) to UVB of planktonic communities in surface waters across contrasting regions of the ocean. We observed here that UVB radiation affects net plankton community production at the ocean surface, imposing a shift in NCP by, on average, 50% relative to the values measured when excluding partly UVB. Our results show that under full solar radiation, the metabolic balance shows the prevalence of net heterotrophic community production. The demonstration of an important effect of UVB radiation on NCP in surface waters presented here is of particular relevance in relation to the increased UVB radiation derived from the erosion of the stratospheric ozone layer. Our results encourage design future research to further our understanding of UVB effects on the metabolic balance of plankton communities.

Comparing marine primary production estimates through different methods and development of conversion equations

“…For instance, modifications of the light field (Kirk, 1994) are observed as the incubations have been conducted with borosilicate bottles, a material that excludes UVB radiation. Indeed, recent analyses comparing estimates derived using quartz and glass bottles have shown that estimates of net community production are affected by the removal of the ambient UVB radiation when glass or plastic materials that filter out UV-B radiation are used, as has been the case for most analyses (Godoy et al, 2012;Agustí et al, 2014;Regaudie-de-Gioux et al, 2014). Furthermore, it is rare for in vitro incubations to be carried out at the correct corresponding environmental temperature.…”

Satellite estimates of net community production indicate predominance of net autotrophy in the Atlantic Ocean

“…In contrast, the photosynthetic rate derived from 'light bottle' incubations reflects production on the day of the incubation maintained in a static and confined (bottle) environment, which can be very different from ambient in situ rates (Westberry et al, 2012). In addition, there may be a bias in these measurements since borosilicate bottles are opaque to UV radiation which can reduce NCP by 45% Regaudie-de-Gioux et al, 2014).…”

Ultraviolet radiation enhances Arctic net plankton community production

“…The trend for UV‐B radiation to shift NCP of plankton communities toward greater net autotrophy in the Arctic is in contrast to results published for communities sampled in the SE Pacific Ocean of the Chilean Coast [ Godoy et al ., ] and in the Atlantic, Mediterranean, and Southern Ocean communities [ Regaudie‐de‐Gioux et al ., ; Agustí et al ., ] where UV‐B radiation generally suppressed NCP, resulting in predominant heterotrophic communities in surface waters. Moreover, the effects of excluding UV‐B radiation on NCP were also of a greater magnitude in the Arctic Ocean, with a reduction of 2.65 ± 0.93 mmol O 2 m −3 d −1 , on average, when UV‐B was excluded, compared to an overall mean increase of NCP by 1.1 ± 0.35 mmol O 2 m −3 d −1 when UV‐B was excluded [ Regaudie‐de‐Gioux et al ., ].…”

“…Whereas the results reported for the Arctic Ocean appear, because of the decrease rather than increase of NCP when UV‐B is excluded, in conflict with previous results [e.g., Godoy et al ., ; Regaudie‐de‐Gioux et al ., ; Agustí et al ., ], this finding is consistent with the analysis of the underlying mechanisms derived from the experiments reported by Agustí et al . [].…”

“…Therefore, the increase in NCP under the midnight sun period is likely explained by a strong inhibition of bacterial respiration during the continuous day of the Arctic summer. Hence, both processes, UV‐B bacterial activity inhibition and lack of a dark period allowing for recovery, may explain the difference, both in magnitude and direction, between the reduced NCP with UV‐B removal found for Arctic communities and the increase in NCP with UV‐B removal found for SE Pacific communities [ Godoy et al ., ] and Mediterranean, Atlantic, and Southern oceans [ Agustí et al ., ; Regaudie‐de‐Gioux et al ., ].…”