1 A bloom of the coccolithophorid, E. Huxleyi, occurred on the eastern Bering Sea shelf during September–October 2000. We examined the impact of this bloom on the CO 2 system in the surface water. Drawdowns of total alkalinity (TAlk) from the values predicted by the TAlk‐salinity conservative mixing relationship reached a maximum of 82.0 μmol kg −1, but was confined to latitudes 57.0°N–61.0°N. Surface water partial pressures of CO 2 ( pCO 2) in excess of 400 μatm, depletion of nitrate + nitrite and low concentrations of silicate were also found, together with the TAlk drawdowns. The relationship between salinity‐normalized TAlk and total CO 2 suggests that the ratio of calcification to photosynthesis during the bloom was approximately 1.0, implying that any CO 2 produced from calcification was balanced by photosynthesis. We discuss the possible cause of the observed high surface water pCO 2 in the TAlk‐drawdown (bloom) area.
Introduction2 Coccolithophorids are a group of phytoplankton that produces plates of CaCO 3 called ‘coccoliths’ surrounding their naked cells. Unlike non‐CaCO 3‐producing‐phytoplanktons, which exclusively produce organic matter by photosynthesis, blooms of coccolithophorids present a unique variation of the CO 2 system in the ocean; in the open ocean, total alkalinity (TAlk) usually shows a linear relationship with salinity, and accordingly is controlled by the physical factors that regulate salinity (water mixing, precipitation and evaporation, etc.). However, if calcification occurs TAlk is reduced distinctly from the value expected from the linear relationship e.g.,.3 During the MR00‐K06 cruise (August–October 2000) by the R/V Mirai of the Japan Marine Science and Technology Center, we encountered aquamarine water in the eastern Bering Sea shelf, which often indicates a coccolithophorid bloom. Microscopic examination revealed that the dominant species of coccolithophorids was E. Huxleyi (approx. 5,000,000 coccolithophorids L −1 by H. Comm.).4 The aim of the present study was to assess the impact of the bloom of E.
Yuki Murata Waters Surface Model
Huxleyi on the CO 2 system in surface waters of the eastern Bering Sea shelf. Observation lines in the eastern Bering Sea shelf. Observations along the Lines 1, 2, and 3 were conducted during the periods 1–7 September, 29 September–3 October and 14–15 August, 2000, respectively. Solid circles on the Line 1 indicate 13 hydrocast stations. For the bloom areas, refer to composite maps of satellite images provided by Oceanic Research and Applications Division, NOAA 6 The pCO 2 was measured by a non‐dispersive infrared analyzer (NDIR).
For atmospheric pCO 2, air from the bow of the ship was sampled into the NDIR. For surface water pCO 2, air equilibrated with water taken from about 4.5 m depth within a showerhead‐type equilibrator, was inputted into the NDIR. The calibration gases used were 240, 290, 310, 380 ppmv in a synthetic air, which are traceable to primary standard gases calibrated by Dr. Keeling of Scripps Institution of Oceanography (SIO). Values of TCO 2 were calibrated against certified reference material (batches 45 or 48) provided by Dr. Dickson of SIO.
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Sea surface temperature (SST) and salinity (SSS) were measured continuously.7 TAlk was calculated from the 2° latitudinal or longitudinal averages of pCO 2 and TCO 2 along the ship's course.8 Along Line 1, nutrients (nitrate + nitrite, phosphate and silicate) were also sampled at 13 hydrocast stations at depths between 0–5 m. Distributions of the CO 2‐System Parameters9 Surface water pCO 2 was highly variable ranging from 220 to 440 μatm along Lines 1 and 2, while atmospheric pCO 2 was nearly constant (358 and 363 μatm for Lines 1 and 2, respectively). Correspondingly, undersaturation (sink) and supersaturation (source) for atmospheric pCO 2 appeared alternately with a small spatial scale. However, the distributions of sinks and sources were generally similar between Lines 1 and 2, despite the temporal and spatial differences between sampling ; between latitudes 57°N–63°N, surface waters were supersaturated, while in the south and north, surface waters were undersaturated. The maximum level of supersaturation for both Lines 1 and 2 was +80 μatm, and the minimum level of undersaturation was approximately −130 μatm.
Drawdowns of TAlk Due to Calcification10 Calculated TAlk and salinity were significantly positively correlated along Line 3, outside the range of the coccolithophorid bloom (n = 60, R 2 = 0.932; P = 0.05; ). While at higher salinities calculated TAlk along Lines 1 and 2 appeared to fit the regression line for Line 3, values for surface waters with salinities less than 30.6‰, deviated from the linear regression line , probably due to mixing with riverine water. The values of TAlk for Lines 1 and 2, in the area of the coccolithophorid bloom, between salinity range 31.0 and 32.0‰ were significantly smaller than the values expected from the linear regression line. Thus, it is inferred that calcification occurred in the salinity range, corresponding to latitudes from 57.0°N to 60.8°N and 56.8°N to 60.8°N along Lines 1 and 2, respectively. The maximum drawdowns of TAlk in the salinity range were 82 μmol kg −1 for Line 1 and 73 μmol kg −1 for Line 2. Relationships Between the Coccolithophorid Bloom and Nutrients11 NO x was almost depleted (0.05–0.26 μmol kg −1) at latitudes north of 58°N along Line 1.
The NO x depleted latitudes corresponded to the TAlk‐drawdown latitudes (57.0°N–60.8°N). SiO 4 showed a sharp decrease of about 20 μmol kg −1 between 55.0°N and 55.5°N, and was smaller than 10 μmol kg −1 at latitudes north of 58°N. There was a significant linear relationship between salinity‐normalized SiO 4 and salinity‐normalized NO x for latitudes south of 55°N (slope = 1.75 ± 0.24; intercept = 6.81 ± 1.18; n = 16; R 2 = 0.948; P 0.41 μmol kg −1.
Yuki Murata Waters Surface Pro
Photosynthesis Versus Calcification12 Theoretically, if photosynthesis occurs simultaneously with calcification, TAlk and TCO 2 change together, and the changing ratio of TAlk to TCO 2, which equals the ratio of calcification to photosynthesis, stays between 1.0 and 2.0.13 Linear regression analysis revealed that TAlk normalized by salinity (nTAlk) changed against TCO 2 normalized by salinity (nTCO 2) at a ratio of 1.1 ± 0.3 (n = 18, R 2 = 0.818, P. Discussion14 In the TAlk‐drawdown (bloom) area, we found surface water pCO 2 exceeded 400 μatm, supersaturated with atmospheric CO 2. The elevated pCO 2 in summer contrasts with the data of Dr. Takahashi (Columbia University; home page address: ), which indicate undersaturation, although other studies ; have reported high pCO 2 levels.
We also observed elevated pCO 2 along the north‐south transect lines in the eastern Bering Sea shelf in 1998 and 1999 (unpublished data). It is worthy to note that extensive coccolithophorid blooms occurred in these years ;. During this previous study calculated TAlk significantly decreased with elevated pCO 2, consistent with the results of the present study. We thus conclude that coccolithophorid blooms in the eastern Bering Sea shelf result in increased surface water pCO 2 levels.15 Increases in pCO 2 levels in coccolithophorid bloom areas have been reported elsewhere ,;;.
Concluding Remarks18 In the present study, we found that surface water pCO 2 exceeded 400 μatm in the coccolithophorid bloom area. As a result, the area acted as a source for atmospheric CO 2 (supersaturation = +80 μatm). The eastern Bering Sea shelf has been known to act as a sink for atmospheric CO 2 in summer due to photosynthesis. Since the supersaturation as a result of the bloom was localized, the bloom of E.
Huxleyi seems to not have a large impact on the planetary‐scale carbon budget. However, such an extensive bloom of E. Huxleyi is not a phenomenon which occurred only in 2000 ;. Now it is inferred that the blooms are a result of climate change, with possible ecosystem‐scale effects in the eastern Bering Sea shelf ;.
Further study is required to investigate what aspects of climate change triggered the blooms.
NAD + is synthesized from tryptophan either via the kynurenine ( de novo ) pathway or via the salvage pathway by reutilizing intermediates such as nicotinic acid or nicotinamide ribose. Quinolinic acid is an intermediate in the kynurenine pathway. We have discovered that the budding yeast Saccharomyces cerevisiae secretes quinolinic acid into the medium and also utilizes extracellular quinolinic acid as a novel NAD + precursor. We provide evidence that extracellular quinolinic acid enters the cell via Tna1, a high-affinity nicotinic acid permease, and thereby helps to increase the intracellular concentration of NAD +. Transcription of genes involved in the kynurenine pathway and Tna1 was increased, responding to a low intracellular NAD + concentration, in cells bearing mutations of these genes; this transcriptional induction was suppressed by supplementation with quinolinic acid or nicotinic acid. Our data thus shed new light on the significance of quinolinic acid, which had previously been recognized only as an intermediate in the kynurenine pathway.