Fecal pellets (FP) are a key component of the biological carbon pump, as they can, under some circumstances, efficiently transfer carbon to depth. Like other forms of particulate organic carbon ...(POC), they can be remineralized in the ocean interior (particularly in the upper 200 m), or alternatively they can be preserved in the sediments. The controls on the attenuation of FP flux with depth are not fully understood, in particular, the relative contributions of zooplankton fragmentation and microbial/zooplankton respiration to FP loss. Collection of sinking particles using Marine Snow Catchers at three ecologically contrasting sites in the Scotia Sea, Antarctica, revealed large differences in POC flux composition (5–96% FP) and flux attenuation despite similar temperatures. To determine the importance of microbial respiration on FP loss in the upper mesopelagic, we made the first ever measurements of small scale oxygen gradients through the boundary layer at the interface of krill FP collected from the Scotia Sea. Estimated carbon-specific respiration rates of microbes within FP (0.010–0.065 d−1) were too low to account for the observed large decreases in FP flux over the upper 200 m. Therefore, the observed rapid declines in downward FP flux in the upper mesopelagic are more likely to be caused by zooplankton, through coprophagy, coprorhexy, and coprochaly. Microbial respiration is likely to be more important in regions of higher temperatures, and at times of the year, or in depths of the ocean, where zooplankton abundances are low and therefore grazing and fragmentation processes are reduced.
Understanding and managing the response of marine ecosystems to human pressures including climate change requires reliable large-scale and multi-decadal information on the state of key populations. ...These populations include the pelagic animals that support ecosystem services including carbon export and fisheries. The use of research vessels to collect information using scientific nets and acoustics is being replaced with technologies such as autonomous moorings, gliders, and meta-genetics. Paradoxically, these newer methods sample pelagic populations at ever-smaller spatial scales, and ecological change might go undetected in the time needed to build up large-scale, long time series. These global-scale issues are epitomised by Antarctic krill ( Euphausia superba ), which is concentrated in rapidly warming areas, exports substantial quantities of carbon and supports an expanding fishery, but opinion is divided on how resilient their stocks are to climatic change. Based on a workshop of 137 krill experts we identify the challenges of observing climate change impacts with shifting sampling methods and suggest three tractable solutions. These are to: improve overlap and calibration of new with traditional methods; improve communication to harmonise, link and scale up the capacity of new but localised sampling programs; and expand opportunities from other research platforms and data sources, including the fishing industry. Contrasting evidence for both change and stability in krill stocks illustrates how the risks of false negative and false positive diagnoses of change are related to the temporal and spatial scale of sampling. Given the uncertainty about how krill are responding to rapid warming we recommend a shift towards a fishery management approach that prioritises monitoring of stock status and can adapt to variability and change.
The boreal copepod
Calanus finmarchicus
sequesters substantial amounts of carbon (C) in the deep layers of the North Atlantic Ocean through their contribution to the “lipid pump.” This pump is driven ...by these zooplankton descending from the surface layers to spend prolonged periods at depth during which time they metabolise substantial lipid reserves and a fraction suffer mortality.
C. finmarchicus
is principally a boreal species but is expatriated by currents flowing northwards into Arctic regions such as the Fram Strait, where it is now able to complete its life cycle. We considered how this expansion to its distributional range adds to the estimated magnitude of the lipid pump. Field sampling in the Fram Strait found
C. finmarchicus
abundance to be spatially variable with high values, equivalent to those reported for core distributional areas further south, found mainly in the eastern region. Lipid reserve levels were sufficient for many individuals to survive the overwintering period and reproduce the following spring. In accordance with abundance patterns, lipid pump magnitude was greater in the Eastern Fram Strait (2.04 g C m
−2
year
−1
) compared to the Western Fram Strait (0.33 g C m
−2
year
−1
). At least for the eastern region, these rates are similar to those reported for this species elsewhere (average of 4.35 g C m
−2
year
−1
). When extrapolated to the wider spatial area of the Fram Strait, the lipid pump generated by this species in this ocean sector amounts to 0.3 Mt C year
−1
. Although constituting a modest proportion of the total
C. finmarchicus
lipid pump of 19.3 Mt C year
−1
, it indicates that the continued northwards expansion of this species will act to increase the size of its lipid pump, which may counteract that lost through the northwards retreat of its Arctic congeners,
Calanus glacialis
and
Calanus hyperboreus
.
Mesopelagic fish have recently been highlighted as an important, but poorly studied component of marine ecosystems, particularly regarding their role in the marine pelagic food webs and ...biogeochemical cycles. Myctophids (Family Myctophidae) are one of the most biomass-dominant groups of mesopelagic fishes, and their large vertical migrations provide means of rapid transfer of carbon to the deep ocean where it can be sequestered for centuries or more. In this study, we develop a simple regression for the respiration rate of myctophid fish using literaturebased wet mass and habitat temperature data. We apply this regression to net haul data collected across the Scotia-Weddell sector of the Southern Ocean to estimate respiration rates of the biomass-dominant myctophid species. Electrona carlsbergi, Electrona antarctica, and Gymnoscopelus braueri made a high contribution (up to 85%) to total myctophid respiration. Despite the lower temperatures of the southern Scotia Sea (−1.46 to 0.95°C), total respiration here was as high (reaching 1.1 mg C m−2 d−1) as in the warmer waters of the mid and northern Scotia Sea. The maximum respiratory carbon flux of the vertically migrating community was 0.05 to 0.28 mg C m−2 d−1, equivalent to up to 47% of the gravitational particulate organic carbon flux in some parts of the Scotia-Weddell region. Our study provides the first baseline estimates of respiration rates and carbon flux of myctophids in the Southern Ocean. However, direct measurements of myctophid respiration, and of mesopelagic fish generally, are needed to constrain these estimates further and incorporate these fluxes into carbon budgets.
The efficiency of the ocean's biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air–sea partitioning of CO2. Despite its ...importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play in the biological carbon pump using both in situ observations and model output. Observed and modelled estimates of fast, slow, and total sinking fluxes are presented from three oceanic sites: the Atlantic sector of the Southern Ocean, the temperate North Atlantic, and the equatorial Pacific oxygen minimum zone (OMZ). We find that observed particle export efficiency is inversely related to primary production likely due to zooplankton grazing, in direct contrast to the model estimates. The model and observations show strongest agreement in remineralization coefficients and BCPeff at the OMZ site where zooplankton processing of particles in the mesopelagic zone is thought to be low. As the model has limited representation of zooplankton-mediated remineralization processes, we suggest that these results point to the importance of zooplankton in setting BCPeff, including particle grazing and fragmentation, and the effect of diel vertical migration. We suggest that improving parameterizations of zooplankton processes may increase the fidelity of biogeochemical model estimates of the biological carbon pump. Future changes in climate such as the expansion of OMZs may decrease the role of zooplankton in the biological carbon pump globally, hence increasing its efficiency.
The abundance and flux of acantharian cysts were recorded for a period of 12 months from December 2012 to 2013 in a sediment trap deployed at 1500 m in the north-eastern Scotia Sea, Southern Ocean. ...Acantharia (radiolarian protists) are found globally, have very dense celestite skeletons, and form cysts which can sink rapidly through the water column. However, they are highly soluble in seawater and have rarely been found to contribute significantly to fluxes of particulate organic carbon (POC) in mesopelagic or bathypelagic zones. We measured fluxes of acantharian cysts of up to 2706 ind. m
−2
day
−1
, which we estimate to drive a POC flux of 5.1 mg C m
−2
day
−1
. These acantharian cyst fluxes are unprecedented in the literature, and accounted for 17% of the annual POC flux at this site (0.5–26.0%). The high fluxes of acantharian cysts (and associated high POC fluxes) measured highlight the pressing need for further research into the life cycles of Acantharia to understand what drives the mass flux of their cysts, and to determine the contribution of Acantharia to the biological carbon pump.
The biological carbon pump is responsible for much of the decadal
variability in the ocean carbon dioxide (CO2) sink, driving the
transfer of carbon from the atmosphere to the deep ocean. A ...mechanistic
understanding of the ecological drivers of particulate organic carbon (POC)
flux is key both to the assessment of the magnitude of the ocean CO2
sink and for accurate predictions as to how this will change with
changing climate. This is particularly important in the Southern Ocean, a
key region for the uptake of CO2 and the supply of nutrients to the
global thermocline. In this study we examine sediment-trap-derived particle
fluxes and stable isotope signatures of carbon (C), nitrogen (N), and
biogenic silica (BSi) at a study site in the biologically productive waters
of the northern Scotia Sea in the Southern Ocean. Both deep (2000 m) and
shallow (400 m) sediment traps exhibited two main peaks in POC, particulate
N, and BSi flux: one in austral spring and one in summer, reflecting periods
of high surface productivity. Particulate fluxes and isotopic compositions
were similar in both deep and shallow sediment traps, highlighting that most
remineralisation occurred in the upper 400 m of the water column.
Differences in the seasonal cycles of isotopic compositions of C, N, and Si
provide insights into the degree of coupling of these key nutrients. We
measured increasing isotopic enrichment of POC and BSi in spring, consistent
with fractionation during biological uptake. Since we observed isotopically
light particulate material in the traps in summer, we suggest
physically mediated replenishment of lighter isotopes of key nutrients from
depth, enabling the full expression of the isotopic fractionation associated
with biological uptake. The change in the nutrient and remineralisation
regimes, indicated by the different isotopic compositions of the spring and
summer productive periods, suggests a change in the source region of
material reaching the traps and associated shifts in phytoplankton community
structure. This, combined with the occurrence of advective inputs at certain
times of the year, highlights the need to make synchronous measurements of
physical processes to improve our ability to track changes in the source
regions of sinking particulate material. We also highlight the need to
conduct particle-specific (e.g. faecal pellets, phytoplankton detritus,
zooplankton moults) isotopic analysis to improve the use of this tool in
assessing particle composition of the sinking material and to develop our
understanding of the drivers of biogeochemical fluxes.
Myctophids (Family Myctophidae, commonly known as the lanternfishes) are critical components of open ocean food webs and an important part of the ocean biological carbon pump, as many species ...actively transport carbon to the deep ocean through their diel vertical migrations. Estimating the magnitude of myctophids’ contribution to the biological carbon pump requires knowledge of their metabolic rate. Unfortunately, data on myctophid metabolic rates are sparse, as they rarely survive being captured and placed in a respirometer. Because of this limitation, many studies estimate myctophid metabolic rates indirectly from body mass and temperature scaling relationships, often extrapolating regressions from global data sets to regional scales. To test the validity of these estimates, we employed a newly developed proxy for mass-specific field metabolic rate (C
resp
: the proportion of metabolically derived carbon in the otolith) based on the stable carbon isotope composition (δ
13
C) of otolith aragonite. We recovered estimates of C
resp
for individuals of 6 species of myctophids from the Scotia Sea, giving a range in C
resp
values from 0.123-0.248. We found that ecological and physiological differences among species are better predictors of variation in C
resp
values than body mass and temperature. We compared our results to estimates of metabolic rates derived from scaling relationships and from measurements of electron transport system activity. When considering myctophids as a whole, we found that estimates of oxygen consumption from different methods are broadly similar; however, there are considerable discrepancies at the species level. Our study highlights the usefulness of metabolic proxies where respirometry is currently unavailable, and provides valuable information on field metabolic rates of myctophids.
Lanternfish are a relatively small but very abundant fish. They live deep in the ocean’s “twilight” zone where there is not much light. A unique community of lanternfish live in the Southern Ocean, ...where they are a key part of the Antarctic food web. Lanternfish also play an important role in moving carbon from the atmosphere into the deep ocean, where it is stored. In this article, we explain current knowledge on Southern Ocean lanternfish, including how they produce their own light! We will also tell you about some mysteries surrounding lanternfish that scientists are yet to solve.
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