Theodore T Packard

Primary production cycle in an upwelling center

Abstract The cycle of nitrogen and carbon productivity of phytoplankton in an upwelling center at 15°S on the coast of Peru was studied during the JOINT-II expedition of the Coastal Upwelling Ecosystems Analysis program. The productivity cycle was characterized by repeated stations at various locations in the upwelling plume, a time series of stations in mid plume, and stations located along drogue tracks. Four zones of physiological condition were distinguished along the axis of the upwelling plume. In Zone I phytoplankton upwelled with nutrient-rich water were initially ‘shifted-down’; in Zone II they underwent light induced ‘shift-up’ to increased nutrient uptake, photosynthesis, and synthesis of macromolecules. In Zone III ambient nutrient concentrations were rapidly reduced, there was a rapid accumulation of phytoplankton biomass in the water column, and rate processes proceeded at maximal rates. In Zone IV ambient nutrient concentrations were significantly decreased, phytoplankton biomass remained high, and limitation of phytoplankton processes was beginning to be observed. Phytoplankton responded to the altered environment by undergoing ‘shift-down’ to lower rates of nutrient uptake, photosynthesis, and macromolecule synthesis. The time and space domain where this entire sequence occurs was relatively small; the cycle from initial upwelling to ‘shift-down’ was completed in 8 to 10 days within 30 to 60 km off the coast.

Deep-ocean metabolic CO2 production: calculations from ETS activity

Abstract Deep-ocean respiration, in terms of CO 2 production, was calculated from measurements of the respiratory electron transport system in microplankton samples from the north central Pacific Ocean and from the northeastern Sargasso Sea. These two data sets support recent arguments that the Pacific Ocean supports more respiration in its subsurface waters than does the Atlantic. Global new production was calculated from these data sets by calculating the CO 2 production rate for the global open ocean below 200 m and then equating this to the new production. The result is 21.9 Gt C per year, 4–11 times greater than previous calculations.

SIZE DEPENDENCE OF GROWTH RATE, RESPIRATORY ELECTRON TRANSPORT SYSTEM ACTIVITY, AND CHEMICAL COMPOSITION IN MARINE DIATOMS IN THE LABORATORY1

The dependence of growth, electron transport system activity and chemical composition on the size of diatoms was examined during the exponential phase of growth. The six different marine centric species compared ranged in volume from 7.7 μm3 to 62 × 105μm3. A size dependence was observed for growth, 14C uptake, respiration and the productivity index (14C/chl a). Although the size dependence of all parameters was similar, the results indicate that on a carbon basis, growth efficiency decreases with increasing size. The C/N and C/chl a ratios were not size dependent. The importance of the surface area to cell volume ratio, and the importance of carbon per unit volume in determining the observed size dependence are discussed.

Differences in biomass structure between oligotrophic and eutrophic marine ecosystems

Abstract A normal trophic pyramid, with most living biomass comprised of plants, is widely assumed to represent marine ecosystems. Oligotrophic and eutrophic environments differ markedly in phytoplankton biomass, but, due to difficulties sampling and quantifying the small, non-plant organisms, it has been difficult to determine the relative plant and non-plant biomass. In eutrophic areas the chlorophyll α/protein ratio (Chl/Pr) of particulate matter, a relative index of phytoplankton to total biomass, approaches that of pure phytoplankton cultures, suggesting that plants constitute most of the biomass. In contrast, in oligotrophic areas the Chl/Pr ratio is low, indicating that most of the biomass consists of bacteria and zooplankton and that an inverted biomass pyramid better describes the system. Thus, ecosystem structure must be fundamentally different between eutrophic and oligotrophic areas.

Formation of the Alboran oxygen minimum zone

Abstract The enhanced oxygen minimum in the western Alboran Sea is the result of a chain of processes starting with nutrient injection into the inflowing Atlantic water at the Strait of Gibraltar. These nutrients originate in the outflowing Levantine Intermediate Water, outflowing Mediterranean deep water, and inflowing North Atlantic Central Water (from 200 m). They are injected into the inflowing Atlantic surface water by strong mixing at the eastern end of the Strait. They move with Atlantic surface waters along the Spanish coast, mix with nutrients upwelling in the northwestern Alboran Sea and stimulate phytoplankton productivity. The organic matter produced by this mechanism is transported both with the anticyclonically flowing waters of the Alboran gyre and with the waters that converge at the center of the gyre. Sedimentation in this convergence zone helps to deliver this organic matter to the Levantine Intermediate. Water where bacteria metabolize it to CO 2 at the expense of the existing oxygen. This mechanism develops the most intense oxygen minimum zone in the Mediterranean Sea.

Sediment metabolism from the northwest African upwelling system

Abstract Sediments off northwest Africa were assayed for activity of the respiratory electron transport system (ETS) and for primary amino nitrogen. ETS activities were used to compute respiratory oxygen consumption, carbon oxidation, and nitrate reduction rates. Activities were correlated with depth of the water column, and their longshore distribution resembled that of euphotic zone phytoplankton productivity. Protein concentrations were closely correlated with ETS activities. Carbon biomass was calculated from protein and compared with other computed values. The carbon oxidation rates accounted for 13% of the regions primary production.

Plankton metabolic activity in the eastern tropical North Pacific

Abstract Respiratory electron transport system (ETS) activity of nannoplankton and zooplankton in the euphotic zone was measured at 14 stations in the eastern tropical North Pacific. In addition, ETS activity and zooplankton biomass were measured from the surface to 3000 m at two stations. Respiration rates were calculated from the ETS activities using empirically derived constants. The respiration rates in the euphotic zone, when compared to the regional productivity, indicate that most of the carbon fixed in the euphotic zone was respired there. This was supported by a vertical respiration budget that indicated that 75% of the respiration from 0 to 3000 m occurred within the euphotic zone and > 90% occurred above 200 m. ETS-derived respiration rates in the deep sea (1 to 3 km) were in agreement with rates calculated from temperature, salinity, and oxygen data using a vertical advection-diffusion model.

Respiration and vertical carbon flux in the Gulf of Maine water column

The transport of carbon from ocean surface waters to the deep sea is a critical factor in calculations of planetary carbon cycling and climate change. This vertical carbon e ux can be calculated by integrating the vertical proe le of the seawater respiration rate but is rarely done because measuring seawater respiration is so dife cult. However, seawater respiratory oxygen consumption is the product of the combined activity of all the respiratory electron transfer systems in a seawater community of bacterioplankton, phytoplankton, and zooplankton. This respiratory electron transfer system (ETS) is the membrane bound enzymatic system that controls oxygen consumption and ATP production in all eukaryots and in almost all bacteria and archaea. As such, it represents potential respiratory oxygen consumption. Exploiting this, we measured plankton-community ETS activity in water column proe les in the Gulf of Maine to give the potential-respiration of the water column. To interpret these potentials in terms of actual seawater respiration we made use of previous measurements of respiratory oxygen consumption and ETS activity in the Gulf of Maine to calculate a ratio of respiratory potential to actual respiration. Armed with this ratio we calculated seawater respiration depth proe les from the ETS activity measurements. These proe les were characterized by: (1) high oxygen consumption rates in the euphotic zone; (2) subsurface maxima near the subsurface chlorophyll maxima (SCM); (3) rapid declines associated with thermoclines; (4) low declining rates below 50 m; (5) and elevated values occasionally near the bottom. Sea surface values ranged from 229 to 489 pmol O 2 min 2 1

Remotely driven thermocline oscillations and denitrification in the eastern South Pacific: The potential for high denitrification rates during weak coastal upwelling

During February–March 1985 denitrification in the ocean off Peru was enhanced in four environments despite relatively weak coastal upwelling winds. They were (i) bottom waters over the shelf, (ii) a deep layer (∼ 300 m) north of ∼ 11°S, (iii) a near surface layer (∼ 40 m) with exceptional nitrite concentrations, and (iv) at relatively shallow depths south of ∼ 11°S. The exceptional 1985 observations may have been related to an unusually shallow thermocline that in turn could have represented a large-scale response to the 1982–1983 el Nino, which was the largest in over 100 years. The super-elevation of the thermocline noted in 1985, however, represented only about a 10% increase in the range of thermocline depth observations in the previous data, suggesting that the 1985 data may represent an extreme development of a recurring situation. During February–March 1985 the average primary production rate was ∼ 2g C m−2day−1, despite the extremely weak upwelling winds (average speed < 4 m−1s), presumably because the elevated thermocline placed high nutrient waters in close proximity to the photic zone. The thermocline waters off Peru are typically low in oxygen, and the low wind speeds apparently restricted the flux of oxygen from the atmosphere into the ocean, since waters with oxygen concentrations of almost zero (< 0.1 ml l−1 ∼ < 4.5 × 10−6M) were sometimes found within 20 m of the sea surface. Since respiration rates decrease with depth and since denitrification is favored by low oxygen tensions, this situation could lead to extremely high denitrification rates in the water column even though primary production might be lower than the average value (∼ 3 g C m−2day−1) due to the weak upwelling winds. Thermocline shoalings like those observed in 1985 are believed to be remotely forced by changes in equatorial winds, and shallow thermocline depths may be a common condition during austral summer. Thus, the February–March 1985 data may shed light on an important and recurring remote influence on denitrification rates in the eastern South Pacific. A major point that emerges from the 1985 observations is that remotely forced thermocline oscillations may have a significant effect on denitrification in the eastern South Pacific Ocean and may, at times, counteract the effect of weak upwelling winds. These data also lend further support to the idea that large temporal variations in the marine denitrification rate can occur in response to relatively small changes in circulation and stratification.

Particulate protein in the Peru upwelling system

Abstract Particulate protein was measured in depth profiles along sections normal to the coast of Peru at 15, 10, and 5°S latitude. A subsurface maximu that coincided with the depth of the secondary nitrite maximum was found between 130 and 230m at 15°S. Protein concentration decreased offshore in the upper 370m, but below 370m horizontal variations were undectable. Vertical profiles show an exponential decrease with depth to 1000m. This rate of decrease was used with oxygen consumption rates to determine mean sinking rates of 1 to 5 m day −1 from 75 to 1000m. Protein was highly correlated with chlorophyll in the euphotic zone and with ETS activity at all depths. Concentrations of protein in the surface waters ranged from 28 to 1157 μg1 −1 ; below 250m concentrations were less than 50 μg1 −1 .