 |
| Titel |
High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest |
| VerfasserIn |
C. A. Frieder, S. H. Nam, T. R. Martz, L. A. Levin |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 9, no. 10 ; Nr. 9, no. 10 (2012-10-12), S.3917-3930 |
| Datensatznummer |
250007328
|
| Publikation (Nr.) |
 copernicus.org/bg-9-3917-2012.pdf |
|
|
|
|
|
| Zusammenfassung |
| Predicting consequences of ocean deoxygenation and ocean acidification for
nearshore marine ecosystems requires baseline dissolved oxygen (DO) and
carbonate chemistry data that are both high-frequency and high-quality. Such
data allow accurate assessment of environmental variability and present-day
organism exposure regimes. In this study, scales of DO and pH variability
were characterized over one year in a nearshore kelp forest ecosystem in the
Southern California Bight. DO and pH were strongly, positively correlated,
revealing that organisms on this upwelling shelf are not only exposed to low
pH but also to low DO. The dominant scale of temporal DO and pH variability
occurred on semidiurnal, diurnal and event (days–weeks) time scales.
Daily ranges in DO and pH at 7 m water depth (13 mab) could be as large as
220 μmol kg−1 and 0.36 units, respectively. Sources of pH and
DO variation include photosynthesis within the kelp forest ecosystem, which
can elevate DO and pH by up to 60 μmol kg−1 and 0.1 units
over one week following the intrusion of high-density, nutrient-rich water.
Accordingly, highly productive macrophyte-based ecosystems could serve as
deoxygenation and acidification refugia by acting to elevate DO and pH
relative to surrounding waters. DO and pH exhibited greater spatial variation
over a 10 m increase in water depth (from 7 to 17 m) than along a 5 km
stretch of shelf in a cross-shore or alongshore direction. Over a three-month
time period, mean DO and pH at 17 m water depth were
168 μmol kg−1 and 7.87, respectively. These values represent
a 35% decrease in mean DO and 37% increase in [H+] relative to
near-surface waters. High-frequency variation was also reduced at depth. The
mean daily range in DO and pH was 39% and 37% less, respectively,
at 17 m water depth relative to 7 m. As a consequence, the exposure history
of an organism is largely a function of its depth of occurrence within the
kelp forest. With knowledge of local alkalinity conditions and high-frequency
temperature, salinity, and pH data, we estimated pCO2 and calcium
carbonate saturation states with respect to calcite and aragonite
(Ωcalc and Ωarag) for the La Jolla kelp forest
at 7 m and 17 m water depth. pCO2 ranged from 246 to
1016 μatm, Ωcalc was always supersaturated, and
Ωarag was undersaturated at the beginning of March for five
days when pH was less than 7.75 and DO was less than
115 μmol kg−1. These findings raise the possibility that the
benthic communities along eastern boundary current systems are currently
acclimatized and adapted to natural, variable, and low DO and pH. Still,
future exposure of coastal California populations to even lower DO and pH may
increase as upwelling intensifies and hypoxic boundaries shoal, compressing
habitats and challenging the physiological capacity of intolerant species. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|