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1.
Optical fractionation of chlorophyll and primary production for coastal waters of the Southern Ocean 总被引:1,自引:1,他引:0
Our objective was to quantify the potential variability in remotely sensed chlorophyll a (Chl a) and primary productivity in coastal waters of the Southern Ocean. From data collected throughout the springs/summers of
1991–1994, we calculated the proportion of water column Chl a and primary productivity within the upper optical attenuation length (K −1
par) and the satellite-weighted depth. The temporal variability was resolved every 2–3 days and was observed to be greater within
years than between years. Three-year averages (n=223) revealed that 10.2 ± 3.6% of total Chl a and 14.8 ± 6.5% of production occurred within satellite-weighted depth in predominantly Case I waters. The average values
were twice as high within K −1
par, 24.1 ± 8% of total Chl a and 34 ± 9% of production respectively. Masked in these long-term averages are very large changes occurring on short time
scales of seasonal blooms. We observed that the patterns of Chl a vertical distribution within blooms are also subject to taxonomic influence and dependent upon the physiological state of
the phytoplankton. Highest proportions of water column Chl a in the first optical depth were measured during the rapid onset of surface cryptophyte blooms each year, i.e. 50% within
K −1
par and 30% above the satellite-weighted depth. Lowest fractions, 6% and 2% of biomass within K −1
par and satellite-weighted depth respectively, were associated with peak bloom conditions independent of taxonomy. Our analyses
suggest that satellite-dependent models of Chl a and subsequent chlorophyll-dependent primary production will be challenging to develop for the near-shore Southern Ocean,
especially given the potentially high natural variability in the vertical distribution of Chl a driven by physical forcing, the photoadaptive abilities of polar phytoplankton, and taxonomic influences.
Accepted: 27 August 1999 相似文献
2.
Rodrigo S. P. de Skowronski Paula F. Gheller Sandra Bromberg Carlos J. David Mônica A. V. Petti Thaïs N. Corbisier 《Polar Biology》2009,32(6):839-851
The spatial and temporal variation of microphytobenthic biomass in the nearshore zone of Martel Inlet (King George Island,
Antarctica) was estimated at several sites and depths (10–60 m), during three summer periods (1996/1997, 1997/1998, 2004/2005).
The mean values were inversely related to the bathymetric gradient: higher ones at 10–20 m depth (136.2 ± 112.5 mg Chl a m−2, 261.7 ± 455.9 mg Phaeo m−2), intermediate at 20–30 m (55.6 ± 39.5 mg Chl a m−2, 108.8 ± 73.0 mg Phaeo m−2) and lower ones at 40–60 m (22.7 ± 23.7 mg Chl a m−2, 58.3 ± 38.9 mg Phaeo m−2). There was also a reduction in the Chl a/Phaeo ratio with depth, from 3.2 ± 3.2 (10–20 m) to 0.7 ± 1.0 (40–60 m), showing a higher contribution of senescent phytoplankton
and/or macroalgae debris at the deeper sites and the limited light flux reaching the bottom. Horizontal differences found
in the biomass throughout the inlet could not be clearly related to hydrodynamics or proximity to glaciers, but with sediment
characteristics. An inter-summer variation was observed: the first summer presented the highest microphytobenthic biomass
apparently related to more hydrodynamic conditions, which causes the deposition of allochthonous material. 相似文献
3.
V. I. Kolmakov O. V. Anishchenko E. A. Ivanova M. I. Gladyshev N. N. Sushchik 《Journal of applied phycology》2008,20(3):289-297
Periphyton (epilithon) gross primary production (GPP) was estimated using the DCMU-fluorescence method in the Yenisei River.
In the unshaded littoral zone, chlorophyll a concentration (Chl a) and GPP value varied from 0.83 to 973.74 mg m−2and 2–304,425 O2 m−2 day−1 (0.64–95 133 mg C m−2 day−1), respectively. Positive significant correlation (r = 0.8) between daily GPP and periphyton Chl a was found. Average ratio GPP:Chl a for periphyton was 36.36 mg C mg Chl a m−2 day−1. The obtained GPP values for the Yenisei River have a high significant correlation with values predicted by a conventional
empirical model for stream periphyton. We concluded that the DCMU-fluorescence method can be successfully used for measuring
of gross primary production of stream phytoperiphyton at least as another useful tool for such studies. 相似文献
4.
Microphytobenthic oxygen production was studied in the Gulf of Fos (French Mediterranean coast) during 1991/1992 using transparent
and dark benthic chambers. Nine stations were chosen in depths ranging from 0.5 to 13 m, which represents more than 60% of
bottoms in the Gulf. Positive net microphytobenthic oxygen production was seasonally detected down to 13 m; the maximum value
attained was 60 mg O2 m−2 h−1 (0.7–0.8 g O2 m−2 d−1) in sediments at 0.5 m depth during spring and winter. Respiration rates were maximum in the sediments located at the mussel
farm (5 m), in the center of the Gulf, with 135 mg O2 m−2 h−1 in spring (3.2 g O2 m−2 d−1); in the other locations, it ranged from 3.3 to 58.2 mg O2 m−2 h−1 (0.08–1.4 g O2 m−2 d−1).
Compared to phytoplankton, microphytobenthos production was higher only in the bottoms < 1 m depth. In deeper bottom waters,
phytoplankton production could be absent due to light limitation, while microphytobenthos was still productive. Phytoplankton
production m−2 was generally higher than microphytobenthic production. Microphytobenthic biomass, higher than phytoplanktonic, varied from
27 to 379 mg Chl a m−2, the maximum in the mussel farm sediments, with the minimum in sandy shallow bottoms. Pigment analysis showed that microphytobenthos
consisted mainly of diatoms (Chl c and fucoxanthin) but other algal groups containing Chl b could become seasonally important. A Principal Component Analysis suggested that the main statistical factors explaining
the distribution of our observations may be interpreted in terms of enrichment in phaeopigments and light; the role of Chl
a appearing paradoxically as secondary in benthic production rates. Phaeopigments are mainly constituted by phaeophorbides,
which indicate grazing processes. The influence of the mussel farm on the oxygen balance is noticeable in the whole Gulf. 相似文献
5.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
6.
Annual and interannual variability in phytoplankton at a permanent station off Kerguelen Islands, Southern Ocean 总被引:4,自引:4,他引:0
From November 1992 to February 1995 a quantitative and qualitative phytoplankton study was conducted at a permanent station
(Kerfix) southwest off the Kerguelen Islands, in the vicinity of the Polar Front (50°40′S–68°25′E). Phytoplankton populations
are low in this area both during summers and winters. They consist, in order of decreasing cell abundance, of pico- and nanoflagellates
(1.5–20 μm), coccolithophorids (<10 μm), diatoms (5–80 μm) and dinoflagellates (6–60 μm). Flagellates form the dominant group
throughout the year and attain the highest summer average of 3.0 × 105 cells l−1. Next in abundance year-round are coccolithophorids with the dominant Emiliania huxleyi (highest summer 1992 average 1.9 × 105 cells l−1), diatoms (summer 1992 average 1.0 × 105 cells l−1) and dinoflagellates (average 3.8 × 104 cells l−1). Winter mean numbers of flagellates and picoplankton do not exceed 8.4 × 104 cells l−1; those of the three remaining algal groups together attain 2 × 104 cells l−1. Summer peaks of diatoms and dinoflagellates are mainly due to the larger size species (>20 μm). The latter group contributes
most to the total cell carbon biomass throughout the year. Dominant diatoms during summer seasons include: Fragilariopsis kerguelensis, Thalassionema nitzschioides, Chaetoceros dichaeta, C. atlanticus, Pseudonitzschia heimii, and P. barkleyi/lineola. This diatom dominance structure changes from summer to summer with only F. kerguelensis and T. nitzschioides retaining their first and second positions. Any one of the co-dominant species might be absent during some summer period.
The variable diatom community structure may be due to southward meandering of the Polar Front bringing “warmer” species from
the north, and to the mixing of the water masses in this area. The entire community structure characterized both during summer
and winters by the dominance of flagellates can be related to deep mixing (ca. 40–200 m) of the water column as the probable
controlling factor.
Received: 13 November 1997 / Accepted: 11 May 1998 相似文献
7.
Bradshaw FJ Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2001,171(1):59-67
A nitrogen balance feeding trial was carried out with the marsupial honey possum, Tarsipes rostratus, using four pollen-honey diets varying in nitrogen content from 9.4 mg · g−1 to 2.3 mg · g−1 dry matter. The dietary maintenance nitrogen requirement (MNR) was determined by regression analysis as 89 ± 21 mg N · kg−0.75 · day−1 and the truly digestible MNR was 79 mg N · kg−0.75 · day−1.. Regressing nitrogen balance on daily nitrogen intake separately for ten males and seven females revealed that the slopes
of the fitted lines did not vary significantly, but the difference in the intercepts approached significance. This suggests
that the MNR for females may be lower than that of males. The nitrogen digestibility of the diet was 76% and the biological
value (BV) was 58%. A comparison of the MNR of the honey possum with that of other marsupials shows that it is indeed much
lower than that of herbivorous macropodid marsupials and is close to that of the sap- and gum-feeding sugar glider, Petarurus breviceps. The endogenous urinary nitrogen excretion (EUN) of the honey possum was 42 mg N · kg−0.75 · day−1 and a regression analysis with other published data showed that the EUN per unit basal heat production is significantly lower
than that of eutherian mammals. Measurements of the actual feeding rates of animals in the field, taken together with the
low MNR, do not lend support to the hypothesis that the honey possum exhibits a reduced rate of reproduction due to a deficiency
in dietary nitrogen. It is possible that the quality of nitrogen provided by pollen, as reflected in its composition of essential
amino acids, may be a limiting factor.
Accepted: 15 September 2000 相似文献
8.
Water and surficial sediment samples of Lake Chascomús and its tributaries were analyzed in order to relate changes in diatom
community structure to chemical variables. Over the course of 13 months of sampling, the lake exhibited major changes in water
level (1.15–1.98 m average depth), total dissolved solids (821–1972 mg l−1), silica (0.098–8.22 mg l−1), and total algal biomass (21.4–145.9 μg Chl a l−1). However, despite these large fluctuations, the diatom species composition was relatively stable. The dominant species in
the water column was always Synedra berolinensis (68.9%–90.1% total frustules), with Fragilaria construens and F. brevistriata as subdominants. In the sediments the latter two species dominated the frustule counts. These results indicate an unusual
floristic stability of this eutrophic ecosystem, with persistent dominance by broadly tolerant, generalist species.
Received: April 24, 2001 / Accepted: January 23, 2002 相似文献
9.
Delorme M Thomas DW 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(2):123-132
Nitrogen (N) and energy (E) requirements of the phyllostomid fruit bat, Artibeus jamaicensis, and the pteropodid fruit bat Rousettus aegyptiacus, were measured in adults that were fed on four experimental diets. Mean daily food intake by A. jamaicensis and R. aegyptiacus ranged from 1.1–1.6 times body mass and 0.8–1.0 times body mass, respectively. Dry matter digestibility and metabolizable
E coefficient were high (81.1% and 82.4%, respectively) for A. jamaicensis and (77.5% and 78.0%, respectively) for R. aegyptiacus. Across the four diets, bats maintained constant body mass with mean metabolizable E intakes ranging from 1357.3 kJ · kg−0.75 · day−1 to 1767.3 kJ · kg−0.75 · day−1 for A. jamaicensis and 1282.6–1545.2 kJ · kg−0.75 · day−1 for R. aegyptiacus. Maintenance E costs were high, in the order of 3.6–5.4 times the basal metabolic rate (BMR). It is unlikely that the E intakes
that we observed represent a true measure of maintenance E requirements. All evidence seems to indicate that fruit bats are
E maximizers, ingesting more E than required and regulating storage by adjusting metabolic output. We suggest that true maintenance
E requirements are substantially lower than what we observed. If it follows the eutherian norm of two times the BMR, fruit
bats must necessarily over-ingest E on low-N fruit diet. Dietary E content did affect N metabolism of A. jamaicensis. On respective low- and high-E diets, metabolic fecal N were 0.492 mg N · g−1 and 0.756 mg N · g−1 dry matter intake and endogenous urinary N losses were 163.31 mg N · kg−0.75 · day−1 and 71.54 mg N · kg−0.75 · day−1. A. jamaicensis required 332.3 mg · kg−0.75 · day−1 and 885.3 mg · kg−0.75 · day−1 of total N on high- and low-E diets, respectively, and 213.7 mg · kg−0.75 · day−1 of truly digestible N to achieve N balance. True N digestibilities were low (29% and 49%) for low- and high-E diets, respectively.
For R. aegyptiacus, metabolic fecal N and endogenous urinary N losses were 1.27 mg N · g−1 dry matter intake and 96.0 mg N · kg−0.75 · day−1, respectively, and bats required 529.8 mg · kg−0.75 · day−1 (total N) or 284.0 mg · kg−0.75 · day−1 (truly digestible N). True N digestibility was relatively low (50%). Based on direct comparison, we found no evidence that
R. aegyptiacus exhibits a greater degree of specialization in digestive function and N retention than A. jamaicensis. When combined with results from previous studies, our results indicate that all fruit bats appear to be specialized in their
ability to retain N when faced with low N diet.
Accepted: 24 November 1998 相似文献
10.
B. M. Spears L. Carvalho R. Perkins M. B. O’Malley D. M. Paterson 《Hydrobiologia》2010,646(1):281-293
Benthic microalgae are known to perform important ecosystem functions in shallow lakes. As such it is important to understand
the environmental variables responsible for regulating community structure, positioning and biomass. We tested the hypothesis
that the positioning (across a depth gradient of 2–22 m overlying water depth) and relative biomass (determined using bulk
and lens tissue harvested chlorophyll (Chl) a concentrations) of the epipelon community would vary independently with season (12 monthly samples) and across natural gradients
of light and habitat disturbance relative to the total benthic algal community (i.e. all viable microalgae in the surface
sediments) in a shallow eutrophic loch. Total sediment microalgal Chl a concentrations (TS-Chl; range: 5–874 μg Chl a g−1 dw) were highest in winter and in the deepest site (20 m overlying water depth), apparently as a result of phytoplanktonic
settling and sediment focussing processes. Epipelic Chl a concentrations (Epi-Chl; range: <0.10–6.0 μg Chl a g−1 dw) were highest in winter/spring, a period when water clarity was highest and TS-Chl lowest. Principal components analysis
highlighted strong associations between Epi-Chl and sites of intermediate depths (2.5–5.5 m) in all seasons except autumn/winter.
Autumn/winter represented the season with the highest average wind speeds preceding sampling, during which the highest Epi-Chl
concentrations were associated with the deepest sites. Epi-Chl was associated with intermediate light and habitat disturbance
during spring/summer and summer/autumn and varied positively with habitat disturbance, only, in autumn/winter and winter/spring.
The epipelon community structure also varied with depth; diatoms dominated shallow water sediments, cyanobacteria dominated
deep water sediments, and sediments at sites of intermediate depth returned the highest biovolume estimates and the most diverse
communities. This study has strengthened the hypothesis that the structure and biomass of benthic microalgal communities in
lakes are regulated by habitat disturbance and water clarity, both of which are expected to respond to climate change and
eutrophication. The degree to which these structural responses reflect functional performance requires clarification. 相似文献
11.
Moro D Bradshaw SD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(8):538-548
A laboratory study investigated the metabolic physiology, and response to variable periods of water and sodium supply, of
two arid-zone rodents, the house mouse (Mus domesticus) and the Lakeland Downs short-tailed mouse (Leggadina lakedownensis) under controlled conditions. Fractional water fluxes for M. domesticus (24 ± 0.8%) were significantly higher than those of L. lakedownensis (17 ± 0.7%) when provided with food ad libitum. In addition, the amount of water produced by M. domesticus and by L. lakedownensis from metabolic processes (1.3 ± 0.4 ml · day−1 and 1.2 ± 0.4 ml · day−1, respectively) was insufficient to provide them with their minimum water requirement (1.4 ± 0.2 ml · day−1 and 2.0 ± 0.3 ml · day−1, respectively). For both species of rodent, evaporative water loss was lowest at 25 °C, but remained significantly higher
in M. domesticus (1.1 ± 0.1 mg H2O · g−0.122 · h−1) than in L. lakedownensis (0.6 ± 0.1 mg H2O · g−0.122 · h−1). When deprived of drinking water, mice of both species initially lost body mass, but regained it within 18 days following
an increase in the amount of seed consumed. Both species were capable of drinking water of variable saline concentrations
up to 1 mol · l−1, and compensated for the increased sodium in the water by excreting more urine to remove the sodium. Basal metabolic rate
was significantly higher in M. domesticus (3.3 ± 0.2 mg O2 · g−0.75 · h−1) than in L. lakedownensis (2.5 ± 0.1 mg O2 · g−0.75 · h−1). The study provides good evidence that water flux differences between M. domesticus and L. lakedownensis in the field are due to a requirement for more water in M. domesticus to meet their physiological and metabolic demands. Sodium fluxes were lower than those observed in free-ranging mice, whose
relatively high sodium fluxes may reflect sodium associated with available food.
Accepted: 16 August 1999 相似文献
12.
A macrozoobenthic community study was conducted in an East Greenlandic fjord (Young Sound, 74°18′N; 20°15′W) during the ice-free
period from July to August in 1996. Grab samples as well as underwater photography were used for quantifying the macrozoobenthos
at water depths between 20 and 85 m. Abundance decreased with depth from 2700 ind. · m−2 at 20 m to 900 ind. · m−2 at 85 m. At a time series station at 35 m, abundance increased from 700 ind. · m−2 in mid-July to 1400 ind. · m−2 in mid-August. Polychaetes dominated in grab samples but bivalves constituted an important part of the benthic fauna, especially
at the shallow part of the depth gradient. Photographs revealed high abundances of large epifaunal species, especially brittle
stars. Diversity was generally high, with around 45 species per 201 individuals, as calculated by Hurlbert's rarefaction term.
A gradual change in community structure with depth was observed, which could be related to variation in sediment composition
and disturbance intensity.
Accepted: 20 May 2000 相似文献
13.
L. E. M. Nery M. A. da Silva A. M. Lauro Castrucci 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(8):624-630
The participation of cyclic nucleotide-dependent intracellular signalling pathways in the pigment translocation induced by
pigment-dispersing hormone (α -PDH) or pigment-concentrating hormone (PCH) was investigated in the erythrophores of the freshwater
shrimp, Macrobrachium potiuna. Cholera toxin, forskolin and dibutyryl cyclic adenosine 3′5′ monophosphate (dbcAMP) were able to induce pigment dispersion
with effective agonist concentrations for half maximal response (EC50 s) of 2.8 · 10−11 mol · l−1, 7.0 · 10−7 mol · l−1 and 3.3 · 10−7 mol · l−1, respectively. KT5720 (10−7 mol · l−1 and 10−6 mol · l−1) significantly shifted the dose response curve to α -PDH to the right. Dibutyryl cyclic guanosine 3′5′ monophosphate (dbcGMP)
was ineffective in inducing either pigment aggregation or dispersion. 2′5′ dideoxyadenosine (DDA) and SQ22,536 essentially
elicit a pigment-aggregating response in a dose-dependent manner. These effects were not due to the activation of purinergic
receptors, since concentrations up to 10−4 mol · l−1 of adenosine and adenosine triphosphate (ATP), and up to 10−3 mol · l−1 of uracil triphosphate (UTP) did not elicit pigment aggregation. In order to verify if PCH decreased cyclic adenosine 3′5′
monophosphate (cAMP) levels, cumulative dose-response curves to PCH in the absence and presence of pertussis toxin and 8-MOM-IBMX
were determined. However, neither drug significantly affected PCH activity. The levels of cAMP in the integument cells of
M. potiuna were significantly increased (P < 0.05) by α -PDH (10−7 mol · l−1) and forskolin (10−6 mol · l−1), but were not affected by PCH (10−7 or 10−10 mol · l−1). In conclusion, α -PDH seems to elicit pigment dispersion through the activation of a Gs-protein coupled receptor resulting
in cAMP increase and cAMP-dependent protein kinase (PKA) activation. Furthermore, although a decrease in cAMP was assumed
to be responsible in turn for the action of PCH, such a decrease could not be directly demonstrated.
Accepted: 11 August 1998 相似文献
14.
Codium fragile (Suringar) Hariot is an edible green alga farmed in Korea using seed stock produced from regeneration of isolated utricles
and medullary filaments. Experiments were conducted to reveal the optimal conditions for nursery culture and out-growing of
C. fragile. Sampling and measurement of underwater irradiance were carried out at farms cultivating C. fragile at Wando, on the southwestern coast of Korea, from October 2004 to August 2005. Growth of erect thalli and underwater irradiance
were measured over a range of depths for three culture stages. During the nursery cultivation stage (Stage I), growth rate
was greatest at 0.5 m depth (0.055 ± 0.032 mm day−1), where the average midday irradiance over 60 days was 924 ± 32 μmol photons m−2 s−1. During the pre-main cultivation stage (Stage II), the greatest growth rate occurred at a depth of 2 m (0.113 ± 0.003 mm day−1) with an average irradiance of 248 ± 116 μmol photons m−2 s−1. For the main cultivation stage (Stage III) of the alga, thalli achieved the greatest increase in biomass at 1 m depth (7.2 ± 1.0 kg
fresh wt m−1). These results suggest that optimal growth at each cultivation stages of C. fragile could be controlled by depth of cultivation rope. 相似文献
15.
Chlorophyll a and nutrient concentrations along with temperature and salinity values were measured at 22 CTD stations along a 735-km transect
running to the northwest of the island of South Georgia, Southern Ocean. Measurements were repeated during five summer surveys
(January and February 1994, January 1996, December 1996, January 1998) and one spring survey (October 1997). The transect
sampled Sub-Antarctic Zone water in the north, Polar Frontal Zone water and Antarctic Zone water in the south. Chlorophyll
a concentrations were lowest to the north of the transect and frequently high (up to 17 mg m−3) in the deep open ocean of the Antarctic Zone. Sub-surface peaks were measured in all zones and chlorophyll a was detectable to a depth of 150 m. There was a clear latitudinal temperature gradient in the near-surface waters (0–50 m),
the warmest water occurring in the north (∼12 °C), and the coolest in the Antarctic Zone (∼2 °C). There was also a well-defined
latitudinal gradient in summer near-surface silicate concentrations (∼2, 4, and 10 mmol m−3 in the Sub-Antarctic Zone, the Polar Frontal Zone and the Antarctic Zone, respectively), increasing to >20 mmol m−3 near South Georgia. Distinct differences in silicate concentrations were also evident in all three zones to a depth of 500 m.
Near-surface nitrate and phosphate concentrations were relatively low to the north of the transect (∼14 and 1 mmol m−3, respectively) and higher in the Polar Frontal Zone and Antarctic Zone (∼18 and 1.4 mmol m−3, respectively). Ammonium and nitrite were restricted to the upper 200 m of the water column, and exhibited sub-surface concentration
peaks, the lowest being in the Sub-Antarctic Zone (0.68 and 0.25 mmol m−3, respectively) and the highest in the Antarctic Zone (1.72 and 0.29 mmol m−3, respectively). Surface (∼6 m) spring nutrient measurements provided an indication of pre-bloom conditions; ammonium and
nitrite concentrations were low (∼0.27 and 0.28 mmol m−3, respectively), while silicate, nitrate and phosphate concentrations were high and similar to previously measured winter
values (e.g. ∼26, 23, 2 mmol m−3, respectively in the Antarctic Zone). Although the values measured were very variable, and there was some evidence of a seasonal
growth progression, the chlorophyll a and nutrient distribution patterns were dominated by intercruise (interannual) factors. Approximate nutrient depletions (spring
minus summer) appeared similar in the Polar Frontal Zone and Antarctic Zone for nitrate and phosphate, while silicate showed
a marked latitudinal increase from north to south throughout the transect. Highest chlorophyll a concentrations coincided with the highest apparent silicate depletions over the deep ocean of the Antarctic Zone. In this
area, relatively warm, easterly flowing Antarctic Circumpolar Current water meets cooler, westerly flowing water that is influenced
by the Weddell-Scotia Confluence and is rich in nutrients, especially silicate.
Accepted: 27 November 1999 相似文献
16.
The Relationship between Phytoplankton Diversity and Community Function in a Coastal Lagoon 总被引:3,自引:0,他引:3
The decrease of biodiversity related to the phenomena of global climate change is stimulating the scientific community towards
a better understanding of the relationships between biodiversity and ecosystem functioning. In ecosystems where marked biodiversity
changes occur at seasonal time scales, it is easier to relate them with ecosystem functioning. The objective of this work
is to analyse the relationship between phytoplankton diversity and primary production in St. André coastal lagoon – SW Portugal.
This lagoon is artificially opened to the sea every year in early spring, exhibiting a shift from a marine dominated to a
low salinity ecosystem in winter. Data on salinity, temperature, nutrients, phytoplankton species composition, chlorophyll
a (Chl a) concentration and primary production were analysed over a year. Modelling studies based on production-irradiance curves
were also conducted. A total of 19 taxa were identified among diatoms, dinoflagellates and euglenophyceans, the less abundant
group. Lowest diversities (Shannon–Wiener index) were observed just before the opening to the sea. Results show a negative
correlation (p<0.05) between diversity and chlorophyll a (Chl a) concentration (0.2–40.3 mg Chl a m−3). Higher Chl a values corresponded to periods when the community was dominated by the dinoflagellate Prorocentrum minimum (>90% of cell abundance) and production was maximal (up to 234.8 mg C m−3 h−1). Maximal photosynthetic rates (Pmax) (2.0–22.5 mg C mg Chl a−1 h−1) were higher under lower Chl a concentrations. The results of this work suggest that decreases in diversity are associated with increases in biomass and
production, whereas increases correspond to opposite trends. It is suggested that these trends, contrary to those observed
in terrestrial and in some benthic ecosystems, may be a result of low habitat diversity in the water column and resulting
competitive pressure. The occurrence of the highest photosynthetic rates when Chl a is low, under some of the highest diversities, suggests a more efficient use of irradiance under low biomass–high diversity
conditions. Results suggest that this increased efficiency is not explained by potential reductions in nutrient limitation
and intraspecific competition under lower biomasses and may be a result of niche complementarity. 相似文献
17.
This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In
total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m2 · kg−1 · 10−2, Dubois surface area 2.01 (0.16) m2, %body fatness 14.6 (3.9)%, V˙O2peak 49.0 (4.8) ml · kg−1 · min−1] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m2 · kg−1 · 10−2, 1.68 (0.13) m2, 20.2 (4.8)%, 43.2 (6.6) ml · kg−1 · min−1, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h−1 followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical
protective clothing (0.29 m2 ·°C · W−1 or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i
m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of
their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min−1 at 105 min (n = 13) compared with 145.1 (14.4) beats · min−1 for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T
re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for
M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric
estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m−2 for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg−1] compared with M [9.45 (1.26) kJ · kg−1]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg−1 for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory
disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can
be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness.
Accepted: 31 October 1997 相似文献
18.
The distribution and biomass of two species of squid, the ommastrephid arrow squid Nototodarus sloanii and the onychoteuthid squid Moroteuthis ingens, were analysed off southern New Zealand. These two species are the most important and abundant species in this region of
the South Pacific Ocean. Data were obtained from extensive NIWA research cruises over 10 years. There was a sharp demarcation
between the distribution of the two species, with N. sloanii occurring predominantly shallower than 600 m, with the greatest biomass less than 300 m. In contrast, M. ingens had the highest biomass between 650 and 700 m and occurred down to 1400 m. The biomass of N. sloanii reached more than 3500 kg · km−2, with an average catch rate of over 186 kg · km−2. In contrast, the biomass of M. ingens was more than an order of magnitude less, with all catch weights less than 200 kg · km−2 and an average catch rate less than 17 kg · km−2. The separation of these two species appeared to be related to depth, temperature and, possibly, salinity. N. sloanii occurred predominantly in warmer, shallower subtropical waters while M. ingens occurred in deeper, cooler subantarctic and antarctic intermediate water masses. The Subtropical Front formed a major barrier
between the distribution of these two squid species.
Accepted: 1 April 2000 相似文献
19.
An investigation into the changing phytoplankton biomass and total water column production during autumn sea ice formation
in the eastern Weddell Sea, Antarctica showed reduced biomass concentrations and extremely low daily primary production. Mean
chlorophyll-a concentration for the entire study period was extremely low, 0.15±0.01 mg.m−3 with a maximum of 0.35 mg.m−3 found along the first transect to the east of the grid. Areas of low biomass were identified as those either associated with
heavy grazing or with deep mixing and corresponding low light levels. In most cases phytoplankton in the <20-μm size classes
dominated. Integrated biomass to 100 m ranged from 7.1 to 28.0 mg.m−2 and correlated positively with surface chlorophyll-a concentrations. Mean PBmax (photosynthetic capacity) and αB (initial slope of the photosynthesis-irradiance curve) were 1.25±0.19 mgC. mgChla
−1.h−1 and 0.042±0.009 mgC.mgChla
−1.h−1.(μmol.m−2.s−1)−1 respectively. The mean index of photoadaptation,I
k, was 32.2±4.0 μmol.m−2.s−1 and photoinhibition was found in all cases. Primary production was integrated to the critical depth (Z
cr) at each production station and ranged from 15.6 to 41.5 mgC.m−2.d−1. It appears that, other than grazing intensity, the relationship between the critical depth and the mixing depth (Z
mix) is an important factor as, ultimately, light availability due both to the late season and growing sea ice cover severely
limits production during the austral autumn. 相似文献
20.
Algal communities and export of organic matter from sea ice were studied in the offshore marginal ice zone (MIZ) of the northern
Barents Sea and Nansen Basin of the Arctic Ocean north of Svalbard by means of ice cores and short-term deployed sediment
traps. The observations cover a total of ten stations within the drifting pack ice, visited over a period of 3 years during
the period of ice melt in May and July. Maximum flux of particulate organic carbon and chlorophyll a from the ice at 1 m depth (1,537 mg C m−2 per day and 20 mg Chl a m−2 per day) exceeded the flux at 30 m by a factor of 2 during spring, a pattern that was reversed later in the season. Although
diatoms dominated the ice-associated algal biomass, flagellates at times revealed similarly high biomass and typically dominated
the exported algal carbon. Importance of flagellates to the vertical flux increased as melting progressed, whereas diatoms
made the highest contribution during the early melting stage. High export of ice-derived organic matter and phytoplankton
took place simultaneously in the offshore MIZ, likely as a consequence of ice drift dynamics and the mosaic structure of ice-covered
and open water characteristic of this region. 相似文献