Ozone Depletion: Icecolors 1990(Cover)
Reference:
R.C.Smith, B.B.Prezelin, R.R.Bidigare, N.P.Boucher, T.Coley, D.Karentz,
S.MacIntyre, H.A.Matlick, D.Menzies, M.Ondrusek, Z.Wan, K.J.Waters.
Ozone depletion: Ultraviolet radiation and phytoplankton biology in Antarctic
waters. Science 255 (5047): 952-959, 1992.
Abstract:
The springtime stratospheric ozone (O3) layer over the Antarctic is thinning by
as much as 50 percent, resulting in increased midultraviolet (UVB) radiation
reaching the surface of the Southern Ocean. There is concern that
phytoplankton communities confined to near-surface waters of the marginal ice
zone will be harmed by increased UVB irradiance penetrating the ocean surface,
thereby altering the dynamics of Antarctic marine ecosystems. Results from a
6-week cruise (Icecolors) in the marginal ice zone of the Bellingshausen Sea
in austral spring of 1990 indicated that as the O3 layer thinned: (i) sea
surface- and depth-dependent rations of UVB irradiances (280 to 320
nanometers) to total irradiance (280 to 700 nanometers) increased and (ii) UVB
inhibition of photosynthesis increased. These and other Icecolors findings
suggest that O3-dependent shifts of in-water spectral irradiances alter the
balance of spectrally dependent phytoplankton processes, including
photoinhibition, photoreactivation, photoprotection, and photosynthesis. A
minimum 6 to 12 percent redfuction in primary production associated with O3
depletion was estimated for the duration of the cruise.
Fig1a:
Ozone hole positions (depicted by 200-DU contours) with respect to the
Antarctic continent (dark area) for 13 and 29 October 1990. The position of
the pack ice (light area), the edge of the MIZ (outer edge of the light area)
during the Icecolors '90 cruise, and the mean position of the Antarctic
convergence within the Southern Ocean (outer edge of the gray area) are also
shown. Cruise location, centered about 64degS 72degW, is indicated by the
black box.
Fig1b:
Ozone concentration (DU) versus time (day of year) for Palmer station and for
the Icecolors '90 sampling area during austral spring 1990. Solid line gives
values derived from UVB measurements on the R.V. Polar Duke. Dashed curves
show values estimated from UVB measurements from the NSF monitoring station at
Palmer, the O3 values from balloon data taken at Palmer, and TOMS data for the
Palmer sampling area (64degS, 72deg30minWW). The comparison shows the
agreeement between UBV-derived values and those obtained by balloon and by
satellite. Data obtained on the R.V>Polar Duke were used for all computations
discussed in the article.
Fig1c:
Ratio of Quvb to total irradiance (Qtotal=Quvb+Quva+Qpar) at the ocean
surface, including variability due to cloud cover, as determined with
shipboard observations during the Icecolors '90 cruise. The Quvb:Qtotal
ration (dashed line) is given for a 4-hour time interval centered on local
noon for each day. Open squares indicate days when in situ biological
moorings were deployed to determine O3-dependent effects on phytoplankton
vitality.
Fig1d:
A comparison of predicted patterns of seasonal change in the ratio of
Quvb:Qtotal for local noon and clear sky conditions at Palmer station, for
surface albedos (A's) of 0.2 and 0.4 and column O3 of 150 (upper two curves)
and 350 DU (lower two curves). These data show the range of natural
variability in this ratio due to seasonal change in solar elevation, indicate
the influence of the O3 hole on this natural variability, and show the values
that this ratio would have for pre-ozone hole, high albedo, clear sky, and
midsummer conditions. Superimposed on the seasonal range of possible
O3-dependent variability in this ratio are the actual fluctuations in
shipboard-measured Quvb:Qtotal (solid curve). Early spring 1990 values of
Quvb:Qtotal exceeded pre-ozone hole maximum values over one-half of the time.
Fig6:
A working model of the photoregulatory interactions of Quvb, Quva, and Qpar on
primary productivity and DNA integrity for phytoplankton communities of the
ANtarctic MIZ. Ik is the saturation parameter for photsynthesis, and Ib is
the photoinhibition onset parameter. SHaded arrow, known direct
photoinhibitory effects on phytoplankton vitality by high fluxes of Quvb,
Quva, and Qpar; open arrow, know processes that diminish the photoinhibitory
effects of Quvb, Quva, and Qpar; wavy arrow, know light-mediated processes
that regular biosynthetic rates; stright arrow, known biosynthetic processes
that regulate photoprotective processes; question mark, hypotesized pathways
of photregulartion consistent with the database of Icecolors.
