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61.
Benthic photosynthesis in submerged Wadden Sea intertidal flats 总被引:3,自引:1,他引:3
Markus Billerbeck Hans Ry Katja Bosselmann Markus Huettel 《Estuarine, Coastal and Shelf Science》2007,71(3-4):704-716
In this study we compare benthic photosynthesis during inundation in coarse sand, fine sand, and mixed sediment (sand/mud) intertidal flats in the German Wadden Sea. In situ determinations of oxygen-, DIC- and nutrient fluxes in stirred benthic chamber incubations were combined with measurements of sedimentary chlorophyll, incident light intensity at the sediment surface and scalar irradiance within the sediment. During submergence, microphytobenthos was light limited at all study sites as indicated by rapid response of gross photosynthesis to increasing incident light at the sea floor. However, depth integrated scalar irradiance was 2 to 3 times higher in the sands than in the mud. Consequently, gross photosynthesis in the net autotrophic fine sand and coarse sand flats during inundation was on average 4 and 11 times higher than in the net heterotrophic mud flat, despite higher total chlorophyll concentration in mud. Benthic photosynthesis may be enhanced in intertidal sands during inundation due to: (1) higher light availability to the microphytobenthos in the sands compared to muds, (2) more efficient transport of photosynthesis-limiting solutes to the microalgae with pore water flows in the permeable sands, and (3) more active metabolic state and different life strategies of microphytobenthos inhabiting sands. 相似文献
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65.
JGOFS has revealed the importance of marine biological activity to the global carbon cycle. Ecological models are valuable tools for improving our understanding of biogeochemical cycles. Through a series of workshops, the North Pacific Marine Science Organization (PICES) developed NEMURO (North Pacific Ecosystem Model Understanding Regional Oceanography) a model, specifically designed to simulate the lower trophic ecosystem in the North Pacific Ocean. Its ability to simulate vertical fluxes generated by biological activities has not yet been validated. Here compare NEMURO with several other lower trophic level models of the northern North Pacific. The different ecosystem models are each embedded in a common three-dimensional physical model, and the simulated vertical flux of POM and the biomass of phytoplankton are compared. The models compared are: (1) NEMURO, (2) the Kishi and Nakata Model (Kishi et al., 1981), (3) KKYS (Kawamiya et al., 1995, 2000a, 2000b), and (4) the Denman model (Denman and Peña, 2002). With simple NPZD models, it is difficult to describe the production of POM (Particulate Organic Matter) and hence the simulations of vertical flux are poor. However, if the parameters are properly defined, the primary production can be well reproduced, even though none of models we used here includes iron limitation effects. On the whole, NEMURO gave a satisfactory simulation of the vertical flux of POM in the northern North Pacific. 相似文献
66.
Hitoshi Kawabata Hisashi Narita Koh Harada Shizuo Tsunogai Masashi Kusakabe 《Journal of Oceanography》2003,59(5):651-661
Thirteen vertical profiles of 226Ra and 222Rn in the near-surface water were obtained in the western North Pacific in winter, and the gas transfer velocities across
the air-sea interface were estimated. The transfer velocities found by applying a steady state model varied widely from 2.1
to 30.2 m day−1 with a mean of 9.4 m day−1. The mean value is almost 5 times higher than that in summer in other oceans, and the maximum value is a record high for
world oceans. This is partly due to the inadequacy of the steady state model, which overestimates when stronger winds blow
in more recent days than the 222Rn half-life of about 4 days. In fact, a strong low pressure zone passed through the station about 2 days earlier, which was
one of the low pressure zones that with a period of develop once a week or so in the northwestern North Pacific in winter.
Instead of steady-state removal, if half of the radon removal occurred sporadically every 7 days, and the last removal took
place two days before the observation, the transfer velocity would be 26 m day−1. Our mean transfer velocity, which is less than 20% different from the steady state value including both overestimated and
underestimated values, 9.4 ± 4.8 m day−1, seems to represent the mean state of this region in winter. This suggests that the gas exchange fluxes under extremely rough
conditions in the open ocean are larger than those estimated by using a transfer velocity equation with a linear or quadratic
relationship with wind speed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
67.
Since the Intermediate Oyashio Water (IOW) gradually accumulates in Sagami Bay, it can reasonably be supposed that the IOW
also flows out from Sagami Bay, even though it may be altered by mixing with other waters. We have occasionally observed a
water less than 34.2 psu with a potential density of 26.8 at the southeastern area off Izu Peninsula in July 1993 by the training
vessel Seisui-maru of Mie University. Observational data supplied by the Japan Meteorological Agency and the Kanagawa Prefectural
Fisheries Experimental Station show that the IOW of less than 34.1 psu was observed at northern stations of the line PT (KJ)
off the Boso Peninsula and to the east of Oshima in the late spring 1993. Based upon these observations, it is concluded that
the IOW flows out from Sagami Bay into the Shikoku Basin along southeastern area off the Izu Peninsula. The less saline water
(<34.2 psu) was also observed to the west of Miyake-jima during the same cruise, and the westward intrusion of IOW from south
of the Boso Peninsula to the Shikoku Basin through the gate area of the Kuroshio path over the Izu Ridge was detected. This
event indicated that the IOW branched south of the Boso Peninsula and flowed into Sagami Bay and/or into the gate area over
the Izu Ridge. The southward intrusion of IOW into the south of the Boso Peninsula is discussed in relation to the latitudinal
location of the main axes of the Kuroshio and the Oyashio.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
68.
The S/V Shoyo, of the Hydrographic Department, Japan Coast Guard, has conducted high-density expendable bathythermograph (XBT)
measurements along the 32.5°N line in the North Pacific every year from 1990 to 1993 as a part of the Japanese-World Ocean
Circulation Experiment (WOCE). These XBT data are analyzed here, focusing on year-to-year variations of the inventory and
core layer temperature (CLT) of the North Pacific subtropical mode water (NPSTMW). Large year-to-year changes are found in
the NPSTMW CLTs estimated in longitudes between 140°E and 160°E. CLT values were found of 17.4°C in 1990, 17.1°C in 1991,
17.3°C in 1992 and 17.6°C in 1993. Inspection of the wintertime westerlies over the formation area and sea surface temperature
distribution revealed that this change in CLT can be qualitatively attributed to the strength of atmospheric cooling in the
formation area in the previous winter. Although a large year-to-year variation of NPSTMW inventory was also found, it is hard
to state any relationship between CLT and atmospheric forcing. There is a possibility that different observational seasons
may affect the inventory. It has also been found that the thermocline depth in 1991 was shallower in the sea area east of
180° than in 1992 and 1993. Associated with this change, the North Pacific central mode water (NPCMW), characterized by thermostad
with temperatures ranging from 14°C to 11°C, appears in the sea area east of 180° in the 1992 and 1993 cross sections. The
1993 cross section, which ranged from the Japanese coast to the west coast of North America, possessed another thermostad
in the surface layer, with a temperature of about 17°C in the eastern part of the cross section, off California.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
69.
Correction method for full-depth current velocity with lowered acoustic Doppler current profiler (LADCP) 总被引:1,自引:0,他引:1
A new method is presented to process and correct full-depth current velocity data obtained from a lowered acoustic Doppler
current profiler (LADCP). The analysis shows that, except near the surface, the echo intensity of a reflected sound pulse
is closely correlated with the magnitude of the difference in vertical shear of velocity between downcast and upcast, indicating
an error in velocity shear. The present method features the use of echo intensity for the correction of velocity shear. The
correction values are determined as to fit LADCP velocity to shipboard ADCP (SADCP) and LADCP bottom-tracked velocities. The
method is as follows. Initially, a profile of velocity relative to the sea surface is obtained by integrating vertical shears
of velocity after low-quality data are rejected. Second, the relative velocity is fitted to the velocity at 100–800 dbar measured
by SADCP to obtain an “absolute” velocity profile. Third, the velocity shear is corrected using the relationship between the
errors in velocity shears and echo intensity, in order to adjust the velocity at sea bottom to the bottom-tracked velocity
measured by LADCP. Finally, the velocity profile is obtained from the SADCP-fitted velocity at depths less than 800 dbar and
the corrected velocity shear at depths greater than 800 dbar. This method is valid for a full-depth LADCP cast throughout
which the echo intensity is relatively high (greater than 75 dB in the present analysis). Although the processed velocity
may include errors of 1–2 cm s−1, this method produced qualitatively good current structures in the Northeast Pacific Basin that were consistent with the
deep current structures inferred from silicate distribution, and the averaged velocities were significantly different from
those calculated by the Visbeck (2002) method. 相似文献
70.
Following our previous study (Sugimoto and Hanawa, 2005b), we further investigate the reason why reemergence of winter sea
surface temperature anomalies does not occur in the North Pacific eastern subtropical mode water (NPESTMW) area, despite its
occurrence in the North Pacific subtropical mode water and North Pacific central mode water areas. We use vertical temperature
and salinity profiles of the World Ocean Circulation Experiment Hydrographic Program and Argo floats with high vertical and
temporal resolution, together with heat flux data through the sea surface. We point out first that one of the causes for non-occurrence
of reemergence is that the thickness of NPESTMW is very thin. In addition to this basic cause, two major reasons are found:
a vigorous mixing in the lower portion of NPESTMW and less heat input from the atmosphere in the warming season. Since, in
the lower portion of NPESTMW and deeper, the stratification is favorable for salt-finger type convection to occur compared
with the other mode water areas, vigorous mixing takes place. This is confirmed by both a large Turner Angle there and the
existence of staircase structures in vertical temperature and salinity profiles. From the viewpoint of heat input, the NPESTMW
area gradually gains heat in the warming season compared with other mode water areas. As a result, NPESTMW cannot be capped
so quickly by the shallow summer mixed layer, and water properties of NPESTMW are to be gradually modified, even in the upper
portion. 相似文献