9 research outputs found
VERTIGO (VERtical Transport In the Global Ocean) : a study of particle sources and flux attenuation in the North Pacific
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1522-1539, doi:10.1016/j.dsr2.2008.04.024.The VERtical Transport In the Global Ocean (VERTIGO) study examined particle sources and
fluxes through the ocean’s “twilight zone” (defined here as depths below the euphotic zone to
1000 m). Interdisciplinary process studies were conducted at contrasting sites off Hawaii
(ALOHA) and in the NW Pacific (K2) during 3 week occupations in 2004 and 2005, respectively.
We examine in this overview paper the contrasting physical, chemical and biological settings and
how these conditions impact the source characteristics of the sinking material and the transport
efficiency through the twilight zone. A major finding in VERTIGO is the considerably lower
transfer efficiency (Teff) of particulate organic carbon (POC), POC flux 500 / 150 m, at ALOHA
(20%) vs. K2 (50%). This efficiency is higher in the diatom-dominated setting at K2 where
silica-rich particles dominate the flux at the end of a diatom bloom, and where zooplankton and
their pellets are larger. At K2, the drawdown of macronutrients is used to assess export and
suggests that shallow remineralization above our 150 m trap is significant, especially for N
relative to Si. We explore here also surface export ratios (POC flux/primary production) and
possible reasons why this ratio is higher at K2, especially during the first trap deployment. When
we compare the 500 m fluxes to deep moored traps, both sites lose about half of the sinking POC
by >4000 m, but this comparison is limited in that fluxes at depth may have both a local and
distant component. Certainly, the greatest difference in particle flux attenuation is in the
mesopelagic, and we highlight other VERTIGO papers that provide a more detailed examination
of the particle sources, flux and processes that attenuate the flux of sinking particles. Ultimately,
we contend that at least three types of processes need to be considered: heterotrophic degradation
of sinking particles, zooplankton migration and surface feeding, and lateral sources of suspended
and sinking materials. We have evidence that all of these processes impacted the net attenuation
of particle flux vs. depth measured in VERTIGO and would therefore need to be considered and
quantified in order to understand the magnitude and efficiency of the ocean’s biological pump.Funding for VERTIGO was provided primarily by research grants
from the US National Science Foundation Programs in Chemical and Biological Oceanography
(KOB, CHL, MWS, DKS, DAS). Additional US and non-US grants included: US Department
of Energy, Office of Science, Biological and Environmental Research Program (JKBB); the
Gordon and Betty Moore Foundation (DMK); the Australian Cooperative Research Centre
program and Australian Antarctic Division (TWT); Chinese NSFC and MOST programs (NZJ);
Research Foundation Flanders and Vrije Universiteit Brussel (FD, ME); JAMSTEC (MCH); New
Zealand Public Good Science Foundation (PWB); and internal WHOI sources and a contribution
from the John Aure and Cathryn Ann Hansen Buesseler Foundation (KOB)
Barium in twilight zone suspended matter as a potential proxy for particulate organic carbon remineralization : results for the North Pacific
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 1673-1683, doi:10.1016/j.dsr2.2008.04.020.This study focuses on the fate of exported organic carbon in the twilight zone at two
contrasting environments in the North Pacific: the oligotrophic ALOHA site (22°45'
N 158°W; Hawaii; studied during June–July 2004) and the mesotrophic Subarctic
Pacific K2 site (47°N, 161°W; studied during July-August 2005). Earlier work has
shown that non-lithogenic, excess particulate Ba (Baxs) in the mesopelagic water
column is a potential proxy of organic carbon remineralization. In general Baxs
contents were significantly larger at K2 than at ALOHA. At ALOHA the Baxs profiles
from repeated sampling (5 casts) showed remarkable consistency over a period of
three weeks, suggesting that the system was close to being at steady state. In contrast,
more variability was observed at K2 (6 casts sampled) reflecting the more dynamic
physical and biological conditions prevailing in this environment. While for both sites
Baxs concentrations increased with depth, at K2 a clear maximum was present
between the base of the mixed layer at around 50m and 500m, reflecting production
and release of Baxs. Larger mesopelagic Baxs contents and larger bacterial production
in the twilight zone at the K2 site indicate that more material was exported from the
upper mixed layer for bacterial degradation deeper, compared to the ALOHA site.
Furthermore, application of a published transfer function (Dehairs et al., 1997)
relating oxygen consumption to the observed Baxs data indicated that the latter were in
good agreement with bacterial respiration, calculated from bacterial production. These
results corroborate earlier findings highlighting the potential of Baxs as a proxy for
organic carbon remineralization.
The range of POC remineralization rates calculated from twilight zone excess
particulate Ba contents did also compare well with the depth dependent POC flux
decrease as recorded by neutrally buoyant sediment traps, except in 1 case (out of 4).
This discrepancy could indicate that differences in sinking velocities cause an
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uncoupling of the processes occurring in the fine suspended particle pool from those
affecting the larger particle pool which sustains the vertical flux, thus rendering
comparison between both approaches risky.This research was supported by Federal Science Policy
Office, Brussels through contracts EV/03/7A, SD/CA/03A, the Research Foundation
Flanders through grant G.0021.04 and Vrije Universiteit Brussel via grant GOA 22, as
well as the US National Science Foundation programs in Chemical and Biological
Oceanography
Particulate aluminium, iron and manganese chemistry at the deep Atlantic boundary layer
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Particulate matter production and consumption in deep mixed layers: observations in a warm-core ring
Particulate matter variability is described in the contect of biological and physical processes in the core waters of WCR 82B between February and late June 1982. WCR 82B formed in mid-February with a probable mixed layer depth of 50 m. A series of heat loss and convective mixing events deepened the mixed layer to >300 m by March and to 400 m by early April 1982. Periods of convective mixing and transient stratification in the deep mixed layer were indicated by chlorophyll, nutrient, and temperature data collected during the last 10 days of April. Seasonal stratification was established by early May, and the core waters of WCR 82B became strongly stratified shallower than 40 m by June.Particulate matter samples were collected from the upper 1000 m by large volumein situ filtration in April and June 1982. Vertical distributions were obtained for particulate dry weight, organic carbon, calcium, biogenic silicon, and phosphorus as well as abundances of >1 mm size fecal matter and fecal pellets.The data show that particle production exceeded particle consumption by zooplankton in the euphotic zone from February to April. However, the particle concentration remained nearly constant in the euphotic zone, but increased between 50 and 400 m during this period. These observations suggest that mixed layer convection in March and April removed a significant fraction of particles from the euphotic zone into the deep thermostad. Analysis of the data shows that 67% of primary produced carbon was mixed into the thermostad during this time. Such conditions were favorable for the growth of herbivorous zooplankton which were dispersed several hundred meters below the surface. Comparisons of the standing stock of particles present in the upper 400 m in late April with supply rates of material due to down mixing suggest that the particle populations in this zone turn over on time scales of 10 days.After onset of seasonal stratification in early May, the down-mixed supply of newly produced carbon to deep thermostad waters was eliminated. Because the rates of euphotic zone particle production and loss were no longer balanced, a bloom of phytoplankton peaking in mid-May may have occurred. Observations showed that particles were removed from the thermostad between April and June, and calculations suggest that this loss (by zooplankton consumption) may have occurred in as short a time as one week following seasonal stratification. Following the removal of utilizable particulate matter, zooplankton shoaled to become concentrated in the upper 50 m by June. The continued high rate of primary production and the strongly increased zooplankton biomass in the upper 50 m in June resulted in enhanced production of fecal material in the upper 40 m. The high rates of zooplankton grazing in June resulted in the removal of most aggregate material by 110 m.These observations demonstrate that the coupling of physical, biological and chemical processes in the upper ocean occurs on time scales as short as 10 days. They also show that particulate matter is a sensitive indicator of the balance between production and removal processes in the upper 1000 m. Our data suggest that (1) zooplankton consumption as opposed to dark respiration is the dominant loss mechanism for phytoplankton carbon mixed below the euphotic zone into deep mixed layers, and (2) the imbalance between production and removal processes in the euphotic zone at the time of stratification caused by the cessation of mixing to depths below the euphotic zone leads to the development of the spring phytoplankton bloom
Particulate matter production and consumption in deep mixed layers: observations in a warm-core ring
Revisiting carbon flux through the ocean's twilight zone
The oceanic biological pump drives sequestration of carbon dioxide in the deep sea via sinking particles. Rapid biological consumption and remineralization of carbon in the "twilight zone" (depths between the euphotic zone and 1000 meters) reduce the efficiency of sequestration. By using neutrally buoyant sediment traps to sample this chronically understudied realm, we measured a transfer efficiency of sinking particulate organic carbon between 150 and 500 meters of 20 and 50% at two contrasting sites. This large variability in transfer efficiency is poorly represented in biogeochemical models. If applied globally, this is equivalent to a difference in carbon sequestration of more than 3 petagrams of carbon per year