Concentrations of floating plastic were measured throughout the Mediterranean Sea to assess whether this basin can be regarded as a great accumulation region of plastic debris. We found that the average density of plastic (1 item per 4 m2), as well as its frequency of occurrence (100% of the sites sampled), are comparable to the accumulation zones described for the five subtropical ocean gyres. Plastic debris in the Mediterranean surface waters was dominated by millimeter-sized fragments, but showed a higher proportion of large plastic objects than that present in oceanic gyres, reflecting the closer connection with pollution sources. The accumulation of floating plastic in the Mediterranean Sea (between 1,000 and 3,000 tons) is likely related to the high human pressure together with the hydrodynamics of this semi-enclosed basin, with outflow mainly occurring through a deep water layer. Given the biological richness and concentration of economic activities in the Mediterranean Sea, the affects of plastic pollution on marine and human life are expected to be particularly frequent in this plastic accumulation region.

The Arctic Ocean is warming at two to three times the global rate 1 and is perceived to be a bellwether for ocean acidification 2,3 . Increased CO 2 concentrations are expected to have a fertilization e ect on marine autotrophs 4 , and higher temperatures should lead to increased rates of planktonic primary production 5 . Yet, simultaneous assessment of warming and increased CO 2 on primary production in the Arctic has not been conducted. Here we test the expectation that CO 2 -enhanced gross primary production (GPP) may be temperature dependent, using data from several oceanographic cruises and experiments from both spring and summer in the European sector of the Arctic Ocean. Results confirm that CO 2 enhances GPP (by a factor of up to ten) over a range of 145-2,099 µatm; however, the greatest e ects are observed only at lower temperatures and are constrained by nutrient and light availability to the spring period. The temperature dependence of CO 2 -enhanced primary production has significant implications for metabolic balance in a warmer, CO 2 -enriched Arctic Ocean in the future. In particular, it indicates that a twofold increase in primary production during the spring is likely in the Arctic.Primary production in the Arctic Ocean supports significant fisheries 6 and renders it an important sink for anthropogenic carbon 2 ; however, climate change has the potential to alter these capacities. Accelerated ice loss is opening surface area across the Arctic, resulting in observations of increased rates of primary production 7 . The reduced salinity caused by melting ice, combined with increasing temperatures, however, increases stratification, restricting turbulent nutrient supply to surface layers 8 . Ice loss also increases surface area for air-sea CO 2 exchange, causing an uptake from the atmosphere into surface waters with already low p CO 2 (ref. 9), and ice melt introduces freshwater with low alkalinity and dissolved inorganic carbon, further lowering the carbon content of surface waters 10 . The surface waters of the Arctic Ocean are largely undersaturated with respect to CO 2 throughout spring and summer 2 . In the European sector of the Arctic Ocean (BarentsGreenland Sea/Fram Strait), p CO 2 varies seasonally by more than 200 µatm, with values as low as 100 µatm in spring months 11 owing to strong net community production associated with the spring bloom of ice algae followed by that of planktonic algae

In situ measurements and aquaria manipulation show that long summer days lead to sustained high pH in Arctic kelp forests.

35Speculation over a global rise in jellyfish populations has become widespread in the 36 scientific literature but until recently the purported 'global increase' had not been tested. 37Here we present a citation analysis of peer-reviewed literature to track the evolution of 38 the current perception of jellyfish increases and identify key papers involved in its 39 establishment. Trend statements and citation threads were reviewed and arranged in a 40 citation network. Trend statements were assessed according their degree of affirmation 41 and spatial scale and the appropriateness of the citations used to support statements was 42 assessed. Analyses showed 48.9% of publications misinterpreted conclusions of cited 43 sources, with a bias towards claiming jellyfish populations are increasing, with one 44 review having the most influence on the network. Collectively, these disparities resulted 45 in a network based on unsubstantiated statements and citation threads. As a community, 46we must ensure our statements about scientific findings in general are accurately 47

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.

The European Sector of the Arctic Ocean is characterized by low CO 2 concentrations in seawater during spring and summer, largely due to strong biological uptake driven by extensive plankton blooms in spring. The spring plankton bloom is eventually terminated by nutrient depletion and grazing. However, low CO 2 concentrations in seawater and low atmospheric resupply of CO 2 can cause episodes during which the phytoplankton growth is limited by CO 2. Here, we show that gross primary production (GPP) of Arctic plankton communities increases from 32 to 72% on average with CO 2 additions in spring. Enhanced GPP with CO 2 additions occur during episodes of high productivity, low CO 2 concentration and in the presence of dissolved inorganic nutrients. However, during summer the addition of CO 2 supresses planktonic Arctic GPP. Events of CO 2 limitation in spring may contribute to the termination of the Arctic spring plankton blooms. The stimulation of GPP by CO 2 during the spring bloom provides a biotic feedback loop that might influence the global role played by the Arctic Ocean as a CO 2 sink in the future.

No abstract

We used inverse modeling to reconstruct major planktonic food web carbon flows in the Atlantic Water inflow, east and north of Svalbard during spring (18-25 May) and summer (9-13 August), 2014. The model was based on three intensively sampled stations during both periods, corresponding to early, peak, and decline phases of a Phaeocystis and diatom dominated bloom (May), and flagellates dominated post bloom stages (August). The food web carbon flows were driven by primary production (290-2,850 mg C m −2 d −1 ), which was channeled through a network of planktonic compartments, and ultimately respired (180-1200 mg C m 2 d −1 ), settled out of the euphotic zone as organic particles (145-530 mg C m −2 d −1 ), or accumulated in the water column in various organic pools. The accumulation of dissolved organic carbon was intense (1070 mg C m −2 d −1 ) during the early bloom stage, slowed down during the bloom peak (400 mg C m −2 d −1 ), and remained low during the rest of the season. The heterotrophic bacteria responded swiftly to the massive release of new DOC by high but decreasing carbon assimilation rates (from 534 to 330 mg C m −2 d −1 ) in May. The net bacterial production was low during the early and peak bloom (26-31 mg C m −2 d −1 ) but increased in the late and post bloom phases (>50 mg C m −2 d −1 ). The heterotrophic nanoflagellates did not respond predictably to the different bloom phases, with relatively modest carbon uptake, 30-170 mg C m 2 d −1 . In contrast, microzooplankton increased food intake from 160 to 380 mg C m 2 d −1 during the buildup and decline phases, and highly variable carbon intake 46-624 mg C m 2 d −1 , during post bloom phases. Mesozooplankton had an initially high but decreasing carbon uptake in May (220-48 mg C m −2 d −1 ), followed by highly variable carbon Frontiers in Marine Science | www.frontiersin.org 1 May 2019 | Volume 6 | Article 244Olli et al.Arctic Food Web Carbon Flow consumption during the post bloom stages (40-190 mg C m −2 d −1 ). Both, micro-and mesozooplankton shifted from almost pure herbivory (92-97% of total food intake) during the early bloom phase to an herbivorous, detritovorous and carnivorous mixed diet as the season progressed. Our results indicate a temporal decoupling between the microbial and zooplankton dominated heterotrophic carbon flows during the course of the bloom in a highly productive Atlantic gateway to the Arctic Ocean.