697 research outputs found
Overview on Ocean Acidification Powerpoint
https://digitalcommons.usm.maine.edu/cbep-presentations/1029/thumbnail.jp
The consequences of human-driven ocean acidification for marine life
Rising atmospheric carbon dioxide is causing a wholesale shift in surface seawater chemistry, potentially threatening many marine organisms that form shells and skeletons from calcium carbonate. Recent papers suggest that the biological consequences of ocean acidification already may be underway and may be more complex, nuanced and widespread than previously thought
Photochemistry, mixing and diurnal cycles in the upper ocean
The interplay between ocean photochemistry and surface boundary-layer physics is explored in a range of analytical and numerical process models. For simple systems, key attributes of the photochemical distributionâdiurnal cycle, surface concentration, and the bulk concentration difference across the âmixed layerââcan be expressed in terms of a small number of physical (vertical diffusivity) and photochemical (turnover timescale and production depth scale) scaling factors. A coupled, 1-D photochemical/physical model is used to examine the more general case with finite mixing rates, variable photochemical production and evolving boundary layer depth. Finite boundary layer mixing rates act to increase both the diurnal cycle and mean concentration at the surface. The diurnal cycle and mean surface concentration are further amplified by coupling between photochemistry and diurnal physics. The daily heating/cooling cycle of the upper ocean can lead to a significant reduction in mixing and boundary-layer depth during the day when photochemical production is at a maximum. Accounting for these effects results in additional surface trapping of photochemically produced species and significant enhancements of the surface diurnal cycle and daily mean. The implications of our model results for field data interpretation and global air-sea flux calculations are also discussed
Scientific outcomes and future challenges of the Ocean Carbon and Biogeochemistry Program
Author Posting. © The Oceanography Society, 2014. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 27, no. 1 (2014): 106â107, doi:10.5670/oceanog.2014.13.The ocean plays a major role in shaping Earth's climate, regulating levels of key atmospheric trace gases such as carbon dioxide on time scales of decades to millennia. Much progress has been made in understanding the global carbon cycle; quantifying major carbon sources, sinks, and transport pathways; and tracking the fate of anthropogenic carbon released from fossil fuel combustion and deforestation. However, many key questions remain regarding the magnitude and evolution of ocean uptake of anthropogenic carbon and the likely biogeochemical and ecosystem responses and feedbacks to future changes in ocean chemistry and climate
Remote sensing observations of ocean physical and biological properties in the region of the Southern Ocean Iron Experiment (SOFeX)
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): C06026, doi:10.1029/2005JC003289.Satellite remote sensing estimates of surface chlorophyll, temperature, wind speed, and
sea ice cover are examined in the region of the Southern Ocean Iron Experiment (SOFeX). Our
objectives are to place SOFeX into a regional context and highlight regional mesoscale spatial
and monthly temporal variability. SOFeX fertilized two patches with iron, one south of the
Antarctic Polar front (PF) and one north of the PF but south of the Subantarctic Front (SAF).
Satellite observable phytoplankton blooms developed in both patches.
The spring sea-ice retreat near the south patch site was delayed in the 2001-2002 season,
in turn delaying the naturally occurring, modest spring bloom in this region. Ambient surface
chlorophyll concentrations for the area surrounding the southern patch during January 2002 are
low (mean 0.26 mg/m3) compared with climatological January values (0.42 mg/m3). Regions
east and west at similar latitudes exhibited higher mean chlorophyll concentrations (0.79 and
0.74 mg/m3, respectively). These modest phytoplankton blooms were likely stimulated by
melting sea-ice via changes in the light-mixing regime and release of iron, and were smaller in
magnitude than the iron-induced bloom within the SOFeX southern patch (> 3 mg/m3). Iron
inputs from melting ice may drive much of the natural spatial and temporal variability within the
seasonal ice zone. Mean chlorophyll concentrations surrounding the SOFeX northern patch site
were similar to climatological values during the SOFeX season. The northern patch was
stretched into a long, thin filament along the southern boundary of the SAF, likely increasing the
mixing/dilution rate with surrounding waters.S. Doney and K.
Moore were supported by NASA grant NAG5-12520 from the NASA Ocean Biogeochemistry
Program
How choice of depth horizon influences the estimated spatial patterns and global magnitude of ocean carbon export flux
Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 4171-4179, doi:10.1029/2017GL076498.Estimated rates and efficiency of ocean carbon export flux are sensitive to differences in the depth horizons used to define export, which often vary across methodological approaches. We evaluate sinking particulate organic carbon (POC) flux rates and efficiency (eâratios) in a global earth system model, using a range of commonly used depth horizons: the seasonal mixed layer depth, the particle compensation depth, the base of the euphotic zone, a fixed depth horizon of 100 m, and the maximum annual mixed layer depth. Within this single dynamically consistent model framework, global POC flux rates vary by 30% and global eâratios by 21% across different depth horizon choices. Zonal variability in POC flux and eâratio also depends on the export depth horizon due to pronounced influence of deep winter mixing in subpolar regions. Efforts to reconcile conflicting estimates of export need to account for these systematic discrepancies created by differing depth horizon choices.Woods Hole Oceanographic Institution (WHOI);
National Science Foundation Grant Number: OCEâ14340002018-10-2
Oceanography : oxygen and climate dynamics
Author Posting. © The Author(s), 2014. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Climate Change 4 (2014): 862-863, doi:10.1038/nclimate2386.Low
oxygen
levels
in
tropical
oceans
shape
marine
ecosystems
and
biogeochemistry
with
climate
change
expected
to
expand
these
regions.
Now,
a
study
indicates
that
regional
dynamics
control
tropical
oxygen
trends,
bucking
projected
global
reductions
in
ocean
oxygen.2015-03-2
The effect of boundary conditions on tracer estimates of thermocline ventilation rates
Using a simple box mixing model, we show that ventilation rate estimates obtained from tracer box models may be significantly smaller than fluid replacement rates. The degree to which a tracer ventilation estimate approaches the actual (fluid) ventilation rate depends on the surface boundary condition for that tracer. Ventilation rates for rapidly exchanging tracers (e.g. 3He) are close to the fluid ventilation rate while tracers with limited surface exchange (e.g. tritium) ventilate more slowly. For box mixing models, the ratio of ventilation rates for limited surface exchange tracers to rapidly exchanging tracers approaches the ratio of summer to winter mixed layer depths. Further, the distribution of rapidly equilibrating tracers more accurately tracks climatological fluctuations in water mass formation rates. Limited surface exchange tracers show a damping proportional to the ratio of summer to winter mixed layer depths. To compare model results with observations, we calculate 3He and tritium ventilation rates from data taken in 1979 in the eastern subtropical North Atlantic. In calculating the tritium ventilation rates, we modify a North Atlantic tritium âsource functionâ (time history of-surface water tritium concentrations), extending previous work using recent data. On shallow density surfaces (Ï \u3c 27.0), the computed tritium ventilation rates are 2â3 times slower than those for 3He, in agreement with climatological ratio of summer to winter mixed layer depths. Deeper in the thermocline, the two tracer estimated ventilation rates converge. This trend may be related to the decreasing effectiveness of 3He gas exchange in equilibrating the deeper winter mixed layers of the more northerly isopycnal outcrops. We conclude that box models using limited surface exchange tracers (e.g. 14C and tritium) can under predict oxygen utilization rates (OUR) by up to 3 times due to differences in tracer boundary conditions, while a tracer like 3He may overestimate OUR by 10â20%
When an ecological regime shift is really just stochastic noise
Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 110 (2013): 2438â2439, doi:10.1073/pnas.1222736110.Populations
of
marine
species
wax
and
wane
over
time
and
space
reflecting
environmental
forcing,
biological
dynamics,
and
in
some
cases
human
perturbations
such
as
fishing,
habitat
destruction
and
climate
change.
The
growing
availability
of
multiâdecadal
observational
records
opens
new
windows
on
how
ocean
ecosystems
function,
but
the
analysis
and
interpretation
of
such
long
time-Ââseries
also
requires
new
mathematical
tools
and
conceptual
models.
Population
time-Ââ
series
often
show
strong
variations
at
decadal
timeâscales,
and
a
central
question
is
whether
this
arises
from
nonâlinear
biological
processes
or
simply
tracking
of
external
physical
variability.
Borrowing
from
climate
research,
Di
Lorenzo
and
Ohman
develop
a
novel
approach
for
deciphering
links
between
physical
forcing
and
biological
response,
using
as
a
test
case
timeâseries
of
marine
zooplankton
abundances
off
the
coast
of
California.The
authors
gratefully
acknowledge
support
from
the
U.S.
National
Science
Foundation
through
the
Palmer
Long
Term
Ecological
Research
(LTER)
project
(http://pal.lternet.edu/)
(NSF
OPP-Ââ0823101)
A three-dimensional, multinutrient, and size-structured ecosystem model for the North Atlantic
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 18 (2004): GB3019, doi:10.1029/2003GB002146.We incorporate multinutrient and size-structured ecosystem dynamics into a three-dimensional ocean general circulation model for the North Atlantic. The model reproduces the magnitude and general spatial and temporal patterns in nutrients, chlorophyll and primary production seen in in situ (BATS, NABE, and OWSI) and satellite (SeaWiFS) data, showing substantial improvements over prior basin-scale simulations. Model skill is evaluated quantitatively against SeaWiFS data using a Taylor diagram approach. Model-data correlation R for the overall surface chlorophyll time-space distribution is âŒ0.6, with comparable model and observed total variability. The agreement relative to satellite-based primary production is somewhat weaker (0.2 < R < 0.5). The simulations capture observed ecological characteristics, e.g., the dominance of picoplankton and episodic diatom blooms in the subtropics, nutrient-controlled plankton succession at higher latitudes, and associated seasonal/depth changes in new and regenerated production and particle export. In a sensitivity experiment that mimics behavior of simpler single-species models, removal of diatom silica limitation leads to major shifts in community structure and export and larger model-data errors similar to previous model studies. Model results also suggest that episodic diatom blooms at BATS may be related to interannual variations in the southward transport of nutrients, mainly SiO3, and plankton cells.Support for this
work was provided by NASA SeaWiFS grant W-19,223 and NSF JGOFS
SMP grant 0222033
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