Comparison of Annual Mean Particle Fluxes between Pacific and Atlantic Mid Latitude Sites

The annual mean export flux of settling particles estimated in this study was compared with values from mid-latitude sites in the Atlantic. The mean total mass fluxes at 1 km water depth measured by the North Atlantic

Figure 7: Sea surface temperature (SST), Chlorophyll-a, phosphate, and dissolved silica versus water depth at Sites 6, 7, and 8 along a transect of 175°E. Data are cited from NEDO (1994).

Figure 7: Sea surface temperature (SST), Chlorophyll-a, phosphate, and dissolved silica versus water depth at Sites 6, 7, and 8 along a transect of 175°E. Data are cited from NEDO (1994).

Bloom Experiment (NABE) for 1 year from 4 April 1989 to 17 April 1990 at approximately 34°N (NABE 34°N, located at 33°49.3'N, 21°00'5W) and 48°N (NABE 48°N, located at 47°42.9'N, 20°51'5W) were 53.2 and 56.7mg m-2 day-1, respectively (Fig. 8). The NABE 34°N value is comparable to that at Site 5 but lower than that at Site 7, while the NABE 48°N value is about one-quarter of that at Site 8. Mean carbonate fluxes were relatively uniform from subtropical to subarctic water masses in the Pacific, and were comparable to those at the NABE sites (approximately 30 mg m-2 day-1). As has already been shown by Berger et al. (1989), the mid-latitude region in the

Lithogenic

Lithogenic

Trap

Site 8

Site 7

Site 5

Site 6

NABE

NABE

Figure 8: Mean daily fluxes (a) and contents (b) of carbonate, OM, opal, and lithogenic matter at Sites 8, 7, 5, and 6 as well as at Atlantic mid-latitude sites. Results from NABE 34°N and 48°N are at 1 km water depth of 33°49.30N, 21°OO05W, and 47°42.90N, 2O°5105W, respectively.

Trap

Site 8

Site 7

Site 5

Site 6

NABE

NABE

Figure 8: Mean daily fluxes (a) and contents (b) of carbonate, OM, opal, and lithogenic matter at Sites 8, 7, 5, and 6 as well as at Atlantic mid-latitude sites. Results from NABE 34°N and 48°N are at 1 km water depth of 33°49.30N, 21°OO05W, and 47°42.90N, 2O°5105W, respectively.

central North Pacific is more productive than that in the central North Atlantic. The OM flux at Site 5 was about 1.5 times that at NABE 34°N, while that at Site 8 was about 3.5 times that at NABE 48°N. The most important contrast between the Pacific and Atlantic was noticed in the biogenic opal flux. The mean biogenic opal fluxes from NABE 34°N and 48°N were 4.5 and 9.7 mg m-2 day-1, respectively, indicating a gradual increase in biogenic opal production from south to north. In contrast, mean biogenic opal fluxes at Sites 5, 7, and 8 were 3.7, 17.5, and 143.4 mg m-2 day-1, respectively, indicate a sharp increase in biogenic opal production from the northern transition zone to the subarctic water mass. In general, the deep water of the North Pacific is enriched with more nutrients such as phosphate and silica than is the deep water of the North Atlantic, because the former has accumulated nutrients and carbon dioxide (through degradation of settling OM) for a longer period of time (Honjo, 1996). These substances are also present in upwelled seawater, leading to higher OM and biogenic opal production rates in the North Pacific. A relatively low flux of biogenic components was observed in pre- and post-bloom episodes in the Atlantic sites. Total mass flux averaged 2.5 mg m-2 day-1 during a post-bloom episode at NABE 34°N, suggesting that biogenic production is limited only during bloom episodes at mid-latitude Atlantic sites.

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