Biology Reference
In-Depth Information
Fig. 19.3
Interannual variation in ocean pH at Tatoosh Island (
n
24,519). pH measurements as
a function of date and time between 2000 and 2007, with significant decline (
P
ΒΌ
0.05). (From
<
Wootton et al.
2008
, with permission of National Academy of Sciences)
including upwelling (Feely et al.
2010
), river outflows (Mathis et al.
2011
), and
metabolic activity of the primary producers themselves (Semesi et al.
2009a
) also
alter pH. Predicting the effects of OA on coastal communities thus requires field
information on the natural daily cycles of pH encountered by organisms in the field.
Coastal ocean pH measurements spanning 8 years around Tatoosh Island in the
eastern Pacific revealed several patterns contrary to the historical perspective that
ocean is well buffered (Wootton et al.
2008
). A diurnal pH oscillation of 0.24 units
is due to daily variation in photosynthesis (CO
2
uptake) which causes pH to
increase during the light and decrease at night due to respiration and diffusion
from the atmosphere which replenish CO
2
(Bensoussan and Gattuso
2007
) causing
a pH decline. A complex seasonal pattern in pH variation was also observed that is
linked to key physical and biological drivers with known mechanistic ties to pH
(cf Wootton et al.
2008
). Looking at the entire temporal span of the data from year
2000 to 2008, however, a general trend of declining pH is apparent which can be
attributed to the effect of increasing atmospheric CO
2
(Fig.
19.3
; Wootton et al.
2008
).
Diurnal variation in pH, total alkalinity (TA), and DIC within a seagrass bed is
related to tidal fluctuations (Semesi et al.
2009a
). During low tide, restricted water
motion, higher irradiance, and temperature caused enhanced rates of seagrass
photosynthesis which resulted in pH increasing from 7.9 to
>
8.9 and a decrease
