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Leiknes T.,Norwegian University of Science and Technology | Striberny A.,University of Tromsø | Tokle N.E.,Planktonic AS | Olsen Y.,Norwegian University of Science and Technology | And 2 more authors.
Journal of Sea Research | Year: 2014

The feeding selectivity of Calanus finmarchicus was studied by carrying out three incubation experiments; two experiments with natural seawater sampled during spring bloom (Exp. 1) and post-bloom conditions (Exp. 2) and a third experiment with cultured dinoflagellates and ciliates (Exp. 3). In the first two experiments a gradient in ciliate concentration was created to investigate the potential for prey density dependent selective feeding of C. finmarchicus. Results of microplankton counts indicated C. finmarchicus to be omnivorous. Diatoms contributed chiefly to the diet during spring bloom conditions. Despite the high microphytoplankton biomass during the spring bloom (Exp. 1), ciliates were selected positively by C. finmarchicus when the ciliate biomass exceeded 6.5μgCL-1. A selection in favor of large conic ciliates such as Laboea sp. and Strombidium conicum was indicated by positive selectivity indices. Ciliates were throughout positively selected by C. finmarchicus during Exp. 2, and selectivity indices indicated a negative selection of diatoms. The results from Exp. 3 showed that C. finmarchicus has the ability to switch from dinoflagellates to ciliates as sole food source, even if the dinoflagellate was offered in surplus. This suggests that other factors, such as nutrition may be of significance for the feeding selectivity of C. finmarchicus. © 2013 Elsevier B.V.


Piccinetti C.C.,Marche Polytechnic University | Ricci L.A.,Marche Polytechnic University | Tokle N.,Planktonic AS | Radaelli G.,University of Padua | And 7 more authors.
Comparative Biochemistry and Physiology - A Molecular and Integrative Physiology | Year: 2012

In the last decades there have been several evidences that traditionally used live preys like rotifers and Artemia salina have nutritional deficiencies that result in a general decrease of fish health, causing anomalies in the development, in growth and in pigmentation. In this study a partial of total replacement of traditional live preys with preserved copepods that represent the natural food of the larvae was evaluated during Solea solea culture. In this study a positive effect of co-feeding preserved copepods in sole larviculture was observed since larvae fed this diet growth and survived better, showed a better tolerance to captive conditions and had a better response to the final thermal/density stress-test with respect to larvae fed a traditional diet. Morphometric data were fully supported by molecular and biochemical ones. Moreover, liver histological investigations, revealed that the inclusion of preserved copepods in the larval diet was able to improve lipid assimilation. In conclusion, preserved copepods may be considered a suitable food for sole when used as a supplement to the traditional diet based on rotifers and Artemia nauplii. © 2011 Elsevier Inc..


Olivotto I.,Marche Polytechnic University | Tokle N.E.,Planktonic AS | Nozzi V.,Marche Polytechnic University | Cossignani L.,University of Perugia | Carnevali O.,Marche Polytechnic University
Aquaculture | Year: 2010

The aim of this study was to evaluate the potential use of preserved copepod as prey in Amphiprion clarkii larviculture. After hatching, A. clarkii larvae were divided in three experimental groups for feeding studies as follows: group A (control group) fed rotifers (Brachionus plicatilis) followed by Artemia nauplii; group B fed a mixed diet of rotifers- Artemia salina nauplii and preserved copepods and group C fed preserved copepods solely. In this study we observed a positive effect of feeding preserved copepods in A. clarkii larviculture as a supplement food to the traditional diet based on rotifers and Artemia nauplii. In group B larvae, fed a combination of rotifers/. Artemia and copepods, a significant increase of insulin like growth factor I and II, peroxisome proliferator activated receptor α-β and thyroid receptor α and β gene expression together with a significant decrease of myostatin gene expression was evidenced by real time PCR compared to the other experimental groups. In this same group we also observed the best results in terms of growth (total length and weight) and survival. These preserved copepods may be considered a suitable food for marine fish larvae larviculture when used as a supplement to the traditional diet based on rotifers and Artemia nauplii. © 2010 Elsevier B.V.


Piccinetti C.C.,Marche Polytechnic University | Tulli F.,University of Udine | Tokle N.E.,Planktonic AS | Cardinaletti G.,University of Udine | Olivotto I.,Marche Polytechnic University
Aquaculture Nutrition | Year: 2014

Considering the well-known problems arising from the use of rotifers and Artemia as live prey in larval rearing in terms of fatty acid deficiencies, the aim of this study was to evaluate a partial or complete replacement of traditional live prey with preserved copepods during the larviculture of gilthead sea bream (Sparus aurata). Sea bream larvae were randomly divided into 4 experimental groups in triplicates: group A larvae (control) fed rotifers followed by Artemia nauplii; group B fed a combined diet (50%) of rotifers-Artemia and preserved copepods; group C fed rotifers followed by preserved copepods; and group D fed preserved copepods solely. Survival and biometric data were analysed together with major molecular biomarkers involved in growth, lipid metabolism and appetite. Moreover, fatty acid content of prey and larvae was also analysed. At the end of 40 days treatment, a stress test, on the remaining larvae, was performed to evaluate the effects of different diets on stress response. Data obtained evidenced a positive effect of cofeeding preserved copepods during sea bream larviculture. Higher survival and growth were achieved in group B (fed combined diet) larvae respect to control. In addition, preserved copepods cofeeding was able to positively modulate genes involved in fish growth, lipid metabolism, stress response and appetite regulation. © 2013 John Wiley & Sons Ltd.


Grant
Agency: European Commission | Branch: H2020 | Program: SME-2 | Phase: BG-12-2015 | Award Amount: 2.00M | Year: 2016

The SME Planktonic has succeeded in cryopreserving marine crustacean nauplii (hereafter called CryoProduct) in large user-friendly entities, and to revive them as live individuals after thawing. The ease-of-use CryoProduct meets the nutritional requirements of fish larvae. A doubling in growth rate and a 25-30% shortening of the live feed period compared to a diet of the suboptimal live feed diets commonly used at marine hatcheries have been demonstrated (large-scale industrial trial, TRL6). With a well-functioning feeding protocol to be developed in the project period, it is expected that performances of the fish larvae will be even better. It will be put effort on optimizing the cryopreservation protocols to achieve a CryoProduct with even better quality than today for improving the performances of fish juveniles. A bio-security evaluation will be performed, and a screening of microorganisms will be needed for the registration of the CryoProduct. To successfully launch the CryoProduct into the EU market, it will be of major importance to scale up the production, to establish efficient logistic systems, identify end-users needs and to provide a reliable commercialisation plan for the best possible market introduction. As the CryoProduct has outstanding performances compared to todays alternatives, we expect a market share of 50% of the live feed market on a longer term. This corresponds to a revenue of more than 100 million . As the market grows 3-4% per year, the market size will double in about 20 years. It is a considerable aquaculture production in the EU. If the product meet the expectations, it will most probably be a major contribution to realize the production potential of marine fish in aquaculture in the EU. This will result in many thousand new jobs, and primarily in the Mediterranean region. The business innovation project fits well to the business strategy of Planktonic, and to the Horizon2020 SME-2 programme under the topic BG-12-2015.


The most important innovation in marine fish aquaculture is the improvement of survival rate and development during the larval stage of the fish. Reasons are that the current nutritional quality of most common live food organisms (rotifers and Artemia nauplii) is inadequate leading to high mortality, deformations and sub-optimal growth during the larval phase of these fish species which limit the overall production. This projects primary objective is to cryopreserve targeted natural zooplankton harvested from the sea, which will be revived for the use as live feed organisms in marine aquaculture. The SME Planktonic has succeeded in cryopreserving marine crustacean nauplii in relatively large scale (entities of up to 200 ml), and to revive them as free swimming organisms (revival rate up to 90%). Because fish larvae are evolutionary adapted to graze on these plankton organisms, it is believed and also documented that it is an optimal diet with respect to nutritional value and performances on the fish growth and survival. Present cryopreservation protocols owned by Planktonic will be further optimized for large scale fish larvae cultivation of both current successful aquaculture species (sea bream and sea bass) and those with requirements of prey of high nutritive value and appropriate size in their early larval phase (e.g. bluefin tuna, long fin yellow tail and Ballan wrasse). Logistics systems for economically feasible shipping of the cryopreserved product within and outside the EU will be assessed, besides procedures for removing market barriers. The world-wide market of Artemia nauplii and rotifers is estimated to about 450 million . Planktonic is aiming at 10% of this market, which will result in a turnover of 45 million . Planktonic will in the proposed project perform a feasibility study with the focus of a business plan, potential partners to succeed with the commercialization and evaluate different technologies for up-scaling of the production.


The present invention relates to a nutritional product comprising a biological material derived from eggs and/or nauplii of stage I of a barnacle and its uses. The invention, especially discloses a feed for early live stages of aquatic animals such as fish or crustaceans comprising isolated eggs and/or nauplii of stage I of a barnacle or a material derived thereof. Methods for harvesting, isolating and preservation of the biological barnacle material are also disclosed.


News Article | November 18, 2015
Site: www.nature.com

Marine sediment core EW0408-85JC is located on the continental slope of the Gulf of Alaska (59° 33.32′ N, 144° 9.21′ W, 682 m). In the modern setting, this site lies near the upper margin of the OMZ, where oxygen concentrations are ~20 μmol kg−1 (Fig. 1). The Gulf of Alaska margin experiences high seasonal productivity during the spring and late summer months, with the highest chlorophyll levels observed along the northern margin32, near the site of EW0408-85JC. The North Pacific drift feeds into the cyclonic Alaskan gyre and Alaskan Coastal Current (ACC), which drives downwelling along the margin33. Details and photographs of the sediment lithology for this core are previously published2. Several sediment cores from various depths from the Northeast Pacific were also employed for the compilation of an oxygen isotope depth transect. Site EW0408-26JC/TC lies along the continental slope off the southeast Alaska margin (56° 96′ N, 136° 43′ W, 1,623 m), near the lower boundary of the OMZ (Fig. 1). Site EW0408-87JC is located under the Gulf of Alaska subpolar gyre, at a depth that lies underneath the modern OMZ (58° 77′ N, 144° 50′ W, 3,680 m). The age model for core EW0408-85JC is based on 36 radiocarbon dates of mixed planktonic foraminifera20 calendar corrected using the Bayesian radiocarbon chronology program BChron34 with the Marine13 database35, assuming a marine reservoir correction of 880 ± 80 yr. The age models for cores EW0408-26JC/TC consist of 10 radiocarbon dates on mixed planktonic foraminifera, calibrated with Calib 7.0 using a marine reservoir correction of 735 ± 50 yr36. The age model for the trigger core of site EW0408-26 is poorly constrained due to low sedimentation rates, bioturbation, and carbonate dissolution in the upper sediments, therefore two tie points to the oxygen isotope stratigraphy of a nearby core with excellent age controls (EW0408-66JC) were used for the Holocene/YD boundary, and a modern age (0 yr bp) is assigned to the top of the core. The age model for core EW0408-87JC is based on 18 mixed planktonic radiocarbon dates calibrated with Calib 7.0 using a marine reservoir correction of 850 ± 100 yr (Extended Data Table 1). One sample was excluded from the age model due to a small reversal. The age model for ODP Site 10191 (Extended Data Fig. 1) is updated with the age model from Lopes et al.17. Benthic radiocarbon ages were measured on mixed species of benthic foraminifera in the same samples as planktonic measurements to give an estimate of ventilation changes between the surface and deep waters at site EW0408-85JC20. Larger benthic-planktonic age differences reflect an increase in reservoir ages of subsurface waters, which may reflect either reduced ventilation rate, decreased preformed radiocarbon in the water mass, or mixing with an older water mass. Benthic ventilation ages were also evaluated using the projection age method37, which accounts for changes in the atmospheric 14C history based on the preformed radiocarbon content of surface waters before subduction, but does not account for subsurface mixing of multiple water masses. Calculated δ18O of seawater (δ18O ) combines planktonic δ18O of Nps or Gb2 with alkenone palaeotemperatures (this paper) using a Gb calibration equation38, followed by correction for the global isotopic effect of changing ice volume39. The depth transect of δ18O includes Nps δ18O data from core EW0408-85JC2 as representative of near-surface conditions. It includes benthic δ18O representative of subsurface conditions in cores EW0408-85JC (682 m depth)2 and EW0408-26JC/TC (1,623 m depth) from Uvigerina peregrina (Uvp), and in core EW0408-87JC (3,680 m depth) from Cibicidoides wuellerstorfi (+0.64 ‰). All were corrected for global ice volume39, but not for temperature. Total lipids were extracted from ~5 g of freeze-dried sediment as per Walinsky et al.40. Linear, alkenone-containing fractions were isolated via urea adduction41 and analysed using capillary gas chromatography with flame ionization detection. Analytical uncertainties in the quantification of C ketone abundance (K37:2, K37:3 and K37:4) include both a mean potential ‘baseline contaminant’ component (positive) and an assumed 5% uncertainty in the integrated area (random). Minimum and maximum estimates of {=(K37:2)/(K37:2 + K37:3)}42 were determined from the uncertainty in K37:2 and K37:3 concentrations. The corresponding uncertainties in temperature estimates are large in samples in the deepest part of the core (corresponding in time to 17.5 – 17.0 ka) due to extremely low K37 concentrations, most likely related high sedimentation rates. Core-top alkenone palaeotemperatures are biased towards summer, and thus are representative of temperatures experienced by the photosynthetic source of these biomarkers43. Various studies have shown that different K37 compounds can be degraded selectively44. Consequently, the sea-surface water temperature proxy, , can be diagenetically biased to some extent. Most lines of evidence indicate preferential degradation of the more unsaturated K37:3. As a result, values, if altered, typically are shifted positively, thereby depicting apparently warmer values. The magnitude of the documented diagenetic warming bias appeared to be ~1 °C or less under the extreme conditions of alkenone degradation experienced in the aerobic burn-down phenomena documented by turbidite records from the Madeira Abyssal Plain45. Bacteria capable of both selective and non-selective aerobic degradation of alkenones have been studied in the laboratory46. In cases where selective alkenone degradation led to a positive shift in values, epoxide derivatives were measured as intermediate products of the process. An empirical calibration of the apparent diagenetic ‘warming’ effect on values caused as a function of these epoxide intermediates has now been defined45. Alkenones and corresponding epoxide intermediates were measured in modern surface sediments collected by multi-core throughout our Southeast Alaska study area43. Interpretation of the results using the laboratory-defined empirical calibration suggested -based SST estimates were biased too warm by as much as 1–2.5 °C43. The perceived warming effect shows a weak correlation (r = +0.26) to the water depth at which each multi-core sample was collected, hinting that the magnitude of the warm bias is directly proportional to the availability of dissolved oxygen. Therefore, it is unlikely that estimated increases in SST during the hypoxic intervals in the Bølling–Allerød interstade (BA) and Holocene are related to changes in the sedimentary diagenetic environment. Observations of similar warming events during the BA and early Holocene from the California margin47 (Extended Data Fig. 9) provide further support that these SST reconstructions reflect regional climate trends rather than local diagenetic imprints. Furthermore, the higher abundances of Epistominella pacifica relative to Bolivina and Bulimina species during cooling episodes in the SST reconstruction, such as the late glacial, Younger Dryas, and early to mid-Holocene (11–6 ka), suggest more oxygenated conditions during cool intervals. These trends are opposite of what would be expected if there was an influence of oxidation on the alkenone SST record, suggesting that a diagenetic warming effect, if present, would most likely act to dampen the observed magnitude of SST changes. SST was also estimated via the temperature index {=(K37:2 − K37:4)/(K37:2 + K37:3 + K37:4)} as calibrated by Prahl et al.43 (Extended Data Fig. 2). The index has been suggested to be a more reliable proxy for SST at temperatures below 8 °C48, 49. The index results in SST estimates that are ~4 °C colder during the late glacial period and ~1 °C warmer during the Holocene period relative to the SST estimates, reflecting the influence of changes in the concentration of tetraunsaturated K37:4, which tends to have higher abundances during glacial times relative to interglacial times (Prahl et al.50 and present study). However, the two SST estimates for the hypoxic intervals are virtually identical, providing further support that temperature estimates for these intervals are not influenced by preferential degradation of more unsaturated compounds. Additionally, the concentration of alkenones are highest during the hypoxic intervals (Extended Data Fig. 2), which not only increases the signal to noise ratio of our analyses (decreasing the associated SST errors), but is also consistent with excellent preservation of organic biomarkers during these events. Average rates of SST change were calculated in a 400-yr window from the palaeotemperature record after interpolating on a 200-yr time step (Extended data Fig. 3) Benthic species abundances were counted from the >150 μm size fraction with sample splits that ranged from 25 – 400 benthic specimens (Extended data Fig. 4). Individual specimens were classified into 12 genera and species categories, and the percent abundance for each species was calculated relative to the total number of benthic species counted. Bulimina and Bolivina are both elongate infaunal benthic genera that are considered indicators of low-oxygen conditions, and sometimes associated with high export productivity51, 52, 53, 54. Bulimina exilis is indicative of the most severe hypoxic/anoxic conditions55. Epistominella pacifica is an epifaunal species that can tolerate intermediate to strong hypoxia and are often found in the upper and lower boundary zones of OMZs54. Uvigerina peregrina can tolerate intermediate to weak hypoxia, but is typically absent from the core of the OMZ. Therefore the relative abundances of these species reflect changes in bottom water oxygen concentrations, with high abundances of Uvigerina peregrina reflecting relatively well-oxygenated conditions, Epistominella pacifica reflecting intermediate hypoxia, Bolivina genera reflecting strong hypoxia, and Bulimina exilis reflecting strongly hypoxic to anoxic conditions. Trace metal concentration data and methods are previously published12, 13. Total metal concentration data (Me ) of Mo and U was converted to excess (xs) values relative to lithogenic background, using Al concentration data in the core and the relationship: Me  = Me  − (Me/Al)  × Al , using average continental crust values of Mo/Al = 0.19 × 10−4 and U/Al = 0.35 × 10−4 (ref. 19). Both raw concentration data and excess concentrations of Mo and U show similar trends, with the greatest enrichments of U and Mo during the hypoxic intervals. Biogenic silica and total organic carbon data and methods are previously published2, 13. The δ15N data and methods are previously published, along with a detailed discussion of various influences that may contribute to the bulk δ15N signature13. A “corrected” marine δ15N record was also calculated by correcting for the δ15N component imparted from terrestrial organic matter13 (Extended Data Fig. 5). This record shows similar overall trends to the raw δ15N record, with enriched δ15N during the BA and early Holocene hypoxic events. Elevated δ15N during the hypoxic intervals is consistent with an increase in nutrient utilization rate, which in this iron-limited setting would likely require an elevated iron source. The δ15N data alone do not prove nutrient utilization; an alternate interpretation is that the high δ15N events during the deglacial transition are an advected signal from low latitudes, where a stronger oxygen minimum zone resulted in water column denitrification56. The viability of the undercurrent transport hypothesis is supported by modern tracer distributions that show California Undercurrent water detectable as far north as Alaska57. Addison et al.13 discounted the undercurrent transport hypothesis as an explanation for deglacial increases in δ15N, simply because the fraction of undercurrent water reaching Alaska today is small (<15% of the subsurface water mass). Implausibly high variations in the tropical source waters (>12 ‰) would be required to explain the ~2‰ δ15N changes in the Gulf of Alaska; such large changes have not been observed in the eastern tropical Pacific58. There is no dynamical mechanism to explain large increases in net pole-ward transport relative to mixing with ambient waters along the flow path that could yield such high-amplitude δ15N changes in the Gulf of Alaska. Additional data argues in favour of a nutrient utilization mechanism to explain the high δ15N events in the Gulf of Alaska. Planktonic foraminiferal δ13C rises during the Bølling–Allerød and early Holocene warming events, sympathetic with high δ15N events (Extended Data Figs 5 and 6). If the δ15N were explained entirely by increased northward advection of high-nutrient, low-oxygen undercurrent waters from the tropics, the warm events should be accompanied by anomalously low δ13C of dissolved inorganic carbon. The same conflict appears for explanations of high productivity by upwelling of deep nutrient rich waters at these times9; upwelling of nutrient-rich waters without an increase in fractional nutrient utilization would yield low δ13C (Extended Data Fig. 6). A regime change occurs in the early Holocene, from a deglacial interval in which δ15N is positively correlated with δ13C (17–9 ka, r2 = 0.51) to a Holocene system in which δ15N and δ13C are weakly negatively correlated (Extended Data Fig. 6). Consideration of changes in atmospheric δ13C (ref. 59) and air-sea equilibrium of the δ13C of carbonate ion as a function of temperature60 strengthens this relationship (Extended Data Fig. 6). The co-occurrence of high δ13C with high δ15N during the deglacial interval points to nutrient utilization rate and carbon export as a key driver of the hypoxic events. This view of nutrient utilization, likely related to removal of iron limitation during the deglacial interval is not inconsistent with the general view of advection of low-oxygen waters northward in the California Undercurrent. Indeed, northward advection of such low oxygen waters near the shelf-slope break would provide a potential reductive source of iron and phosphate24 from sediments, and would be part of a self-sustaining feedback in the northeast Pacific in which initial hypoxia would be sustained and strengthened by iron-fuelled export productivity. Iron can be transported relatively long distances in the subsurface ocean in the colloidal (essentially non-sinking) fraction61. Such a mechanism is consistent with sea-level rise onto the continental shelves as a possible iron source1, and addresses concerns that isostatic rebound puts the local sea-level record in the northern Gulf of Alaska out of synch with the hypoxic events9. The collection of multiple proxies within the same core allows for a precise examination of the timing of redox changes relative to changes in oceanographic conditions and export productivity (Extended Data Fig. 7). The transition to laminated sediments during the BA occurs with a sharp sedimentological boundary at 681 cm core depth2. The laminations are closely associated with high weight percentages of biogenic opal, consistent with high export of diatoms. The laminated intervals are also clearly defined in the X-ray computed tomography (CT) grey scan data, which largely tracks sediment density as a function of the biogenic to lithogenic fraction, with low values indicating times of high biogenic input2. The initial increase in SST precedes the increase in opal and the onset of laminations during the BA hypoxic event; temperatures >10 °C are associated with the interval of high diatom abundances. The increase in U and Mo occurs slightly before (2 – 5 cm) the increases in biogenic opal, TOC, and the decrease in CT grey scale. This may reflect a progression towards low oxygen conditions before the increase in export productivity. It is possible that such small depth offsets between the increase in trace metals and organic matter concentration may reflect preserved redox gradients in the sediment column, and thus not truly represent offsets in the time domain. However, all these proxies are emplaced within the bioturbed mixed layer and within a few cm of the seafloor during laminated intervals62, so depth offsets between proxies should be minor. There are no discernible leads or lags between the increase in SST and export productivity for the Holocene hypoxic event. However, in this interval, the increase in U and Mo appear to slightly lag the increase in biogenic silica and the transition to low-oxygen benthic fauna. The Holocene laminated interval is not as precisely defined as the onset of the BA laminations, partly due to weaker (slightly mottled) laminations, making the evaluation of depth offsets in the proxy data less reliable than for the BA sequence. The switch from oxic to hypoxic/anoxic-tolerant benthic fauna occurs abruptly near the onset of laminations for both the BA and Holocene events. However, low-oxygen benthic species dominate the faunal assemblages well after the termination of laminations and the decrease in biogenic silica. Similar trends can be seen in the trace metal data. This concordance may indicate that low-oxygen conditions persisted even after the decline in export productivity and the cessation of laminations. This is consistent with a hysteresis-like response in the benthos, with an abrupt threshold transition to a hypoxic regime, followed by a more gradual return to an oxic regime with a diversity of benthic fauna63. Some upward mixing of older hypoxic fauna by bioturbation could have occurred when oxic conditions returned, however, this is unlikely to account for the high abundances (60 – 80%) of low-oxygen fauna that persisted in these intervals. Based on this sequence of events, it appears most probable that sea surface warming lead to a reduction of dissolved oxygen in the subsurface through the combined effects of reduced oxygen solubility and enhanced thermal stratification. Benthic fauna assemblages from a deeper site in the Gulf of Alaska (near the lower boundary of the OMZ) suggest a gradual progression towards hypoxia starting at 16 ka, followed by an abrupt onset of laminations at the transition into the BA (Extended Data Fig. 8). The initial reduction of dissolved oxygen in the subsurface would have intensified the OMZ, leading to an expanded area of hypoxic shelf sediments (Fig. 3). A shoaling of the upper boundary of the OMZ to ~300 m during the BA hypoxic event has been documented in benthic faunal assemblages from the California Borderland basins64. The supply of sedimentary iron is thought to be most efficient in a redox window where neither oxygen nor sulfide is present19, making such “new hypoxic zones” prime candidates for the release of bioavailable iron, especially in the shallower depths where iron can be more easily upwelled to the surface, as occurs in offshore regions of the Gulf of Alaska. Additional sources of iron include freshwater runoff charged with glacial rock flour. Such supplies of iron could have helped to fuel primary productivity, enhanced export productivity, and further depleted subsurface ocean concentrations, leading to a threshold-like feedback effect to amplify ocean deoxygenation. The timing of the North Pacific hypoxic events approximately coincided with two intervals of abrupt increase in atmospheric N O (ref. 65) and a cessation in the rise of atmospheric CO (refs 66, 67) (Extended Data Fig. 9). The widespread expansion of hypoxic zones in the North Pacific could have led to denitrification, contributing to the two abrupt increases in atmospheric N O, while the enhanced export flux and burial of organic carbon may have helped to stabilize the rise in atmospheric CO (ref. 4). Thus, the temperature evolution of the North Pacific could play a prominent role in the regulation of multiple greenhouse gases. Initial deglacial warming could promote out-gassing of deep-ocean respired carbon. Continuous and/or abrupt warming could have pushed large areas of the North Pacific across thresholds of hypoxia, in which the cycling of nutrients and carbon was fundamentally altered, contributing to expansive denitrification and the release of N O gases. However, the development of widespread hypoxia may ultimately act as a negative feedback on rising CO and global warming, with the release of nutrients from hypoxic sediments acting to stimulate surface productivity (in particular, diatoms with high efficiency for carbon export27) and the decrease in water column oxygen concentration helping to promote carbon burial (Fig. 3). Thus, thresholds of hypoxia in the North Pacific linked to ocean warming have the potential to switch this region from a source to sink of carbon.

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