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The third primary production algorithm round robin (PPARR3) compares output from 24 models that estimate depthintegrated primary production from satellite measurements of ocean color, as well as seven general circulation models (GCMs) coupled with ecosystem or biogeochemical models. Here we compare the global primary production fields corresponding to eight months of 1998 and 1999 as estimated from common input fields of photosynthetically-available radiation (PAR), sea-surface temperature (SST), mixed-layer depth, and chlorophyll concentration. We also quantify the sensitivity of the ocean-color-based models to perturbations in their input variables. The pair-wise correlation between ocean-color models was used to cluster them into groups or related output, which reflect the regions and environmental conditions under which they respond differently. The groups do not follow model complexity with regards to wavelength or depth dependence, though they are related to the manner in which temperature is used to parameterize photosynthesis. Global average PP varies by a factor of two between models. The models diverged the most for the Southern Ocean, SST under 10 C, and chlorophyll concentration exceeding 1 mg Chl m À3 . Based on the conditions under which the model results diverge most, we conclude that current ocean-color-based models are challenged by high-nutrient low-chlorophyll conditions, and extreme temperatures or chlorophyll concentrations. The GCM-based models predict comparable primary production to those based on ocean color: they estimate higher values in the Southern Ocean, at low SST, and in the equatorial band, while they estimate lower values in eutrophic regions (probably because the area of high chlorophyll concentrations is smaller in the GCMs). Further progress in primary production modeling requires improved understanding of the effect of temperature on photosynthesis and better parameterization of the maximum photosynthetic rate. r

Abstract. Error-quantified, synoptic-scale relationships between chlorophyll-a (Chl-a) and phytoplankton pigment groups at the sea surface are presented. A total of ten pigment groups were considered to represent three Phytoplankton Size Classes (PSCs, micro-, nano-and picoplankton) and seven Phytoplankton Functional Types (PFTs, i.e. diatoms, dinoflagellates, green algae, prymnesiophytes (haptophytes), pico-eukaryotes, prokaryotes and Prochlorococcus sp.). The observed relationships between Chl-a and PSCs/PFTs were well-defined at the global scale to show that a community shift of phytoplankton at the basin and global scales is reflected by a change in Chl-a of the total community. Thus, Chl-a of the total community can be used as an index of not only phytoplankton biomass but also of their community structure. Within these relationships, we also found nonmonotonic variations with Chl-a for certain pico-sized phytoplankton (pico-eukaryotes, Prokaryotes and Prochlorococcus sp.) and nano-sized phytoplankton (Green algae, prymnesiophytes). The relationships were quantified with a leastsquare fitting approach in order to enable an estimation of the PFTs from Chl-a where PFTs are expressed as a percentageCorrespondence to: T. Hirata (tahi@ees.hokudai.ac.jp) of the total Chl-a. The estimated uncertainty of the relationships depends on both PFT and Chl-a concentration. Maximum uncertainty of 31.8% was found for diatoms at Chla = 0.49 mg m −3 . However, the mean uncertainty of the relationships over all PFTs was 5.9% over the entire Chl-a range observed in situ (0.02 < Chl-a < 4.26 mg m −3 ). The relationships were applied to SeaWiFS satellite Chl-a data from 1998 to 2009 to show the global climatological fields of the surface distribution of PFTs. Results show that microplankton are present in the mid and high latitudes, constituting only ∼10.9% of the entire phytoplankton community in the mean field for 1998-2009, in which diatoms explain ∼7.5%. Nanoplankton are ubiquitous throughout the global surface oceans, except the subtropical gyres, constituting ∼45.5%, of which prymnesiophytes (haptophytes) are the major group explaining ∼31.7% while green algae contribute ∼13.9%. Picoplankton are dominant in the subtropical gyres, but constitute ∼43.6% globally, of which prokaryotes are the major group explaining ∼26.5% (Prochlorococcus sp. explaining 22.8%), while pico-eukaryotes explain ∼17.2% and are relatively abundant in the South Pacific. These results may be of use to evaluate global marine ecosystem models.

[1] In an attempt to examine the characteristic behavior of asperities, we studied the source processes of large interplate earthquakes offshore of the Tohoku district, northeastern Japan, over the past 70 years. In this area, earthquakes of M7 class have a recurrence interval of about 30 years. Seismic observation using a strong-motion seismometer has been carried out by the Japan Meteorological Agency since the beginning of the 1900s. We collected these seismograms in order to make a waveform inversion. On the basis of the derived heterogeneous fault slip, we identified large slip areas (asperities) for eight earthquakes which occurred after 1930, and we constructed an asperity map. The typical size of individual asperities in northeastern Japan is M7 class, and an M8 class earthquake can be caused when several asperities are synchronized. We propose that the patterns of asperity distribution beneath offshore Tohoku fall into three different categories. In the northern part (40°-41.3°N) the seismic coupling in the asperity is almost 100%, and the size is large. In the central part (39°-40°N), little seismic moment has been released by large earthquakes, and the asperity size is small. In the southern part (37.8°-39°N) the seismic coupling is medium. The weak seismic coupling may be related to submarine topographical features and to the sediment and water along the subducting plate. Our results also suggest a general tendency for the asperities to be located away from the hypocenters (initial break), with aftershocks occurring in the area surrounding the asperity.INDEX TERMS: 7215 Seismology: Earthquake parameters; 7209 Seismology: Earthquake dynamics and mechanics; 7230 Seismology: Seismicity and seismotectonics; 8150 Tectonophysics: Plate boundary-general (3040); KEYWORDS: asperity, source process, historical seismograms Citation: Yamanaka, Y., and M. Kikuchi (2004), Asperity map along the subduction zone in northeastern Japan inferred from regional seismic data,

[1] Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (±1s) downward flux of organic matter across 75 m depth is 17 ± 6 Pg C yr À1 . Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.

We compared the 13 models participating in the Ocean Carbon Model Intercomparison Project (OCMIP) with regards to their skill in matching observed distributions of CFC-11. This analysis characterizes the abilities of these models to ventilate the ocean on timescales relevant for anthropogenic CO uptake. We found a large range in the modeled global inventory (AE30%), mainly due to differences in ventilation from the high latitudes. In the Southern Ocean, models differ particularly in the longitudinal distribution of the CFC uptake in the intermediate water, whereas the latitudinal distribution is mainly controlled by the subgrid-scale parameterization. Models with isopycnal diffusion and eddy-induced velocity parameterization produce more realistic intermediate water ventilation. Deep and bottom water ventilation also varies substantially between the models. Models coupled to a sea-ice model systematically provide more realistic AABW formation source region; however these same models also largely overestimate AABW ventilation if no specific parameterization of brine rejection during sea-ice formation is included. In the North Pacific Ocean, all models exhibit a systematic large underestimation of the CFC uptake in the thermocline of the subtropical gyre, while no systematic difference toward the observations is found in the subpolar gyre. In the North Atlantic Ocean, the CFC uptake is globally underestimated in subsurface. In the deep ocean, all but the adjoint model, failed to produce the two recently ventilated branches observed in the North Atlantic Deep Water (NADW). Furthermore, simulated transport in the Deep Western Boundary Current (DWBC) is too sluggish in all but the isopycnal model, where it is too rapid. Ó

Subducting seamounts are thought to increase the normal stress between subducting and overriding plates. However, recent seismic surveys and laboratory experiments suggest that interplate coupling is weak. A seismic survey in the Japan Trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude M approximately 7. Both observed seismicity and the pattern of rupture propagation during the 1982 M 7.0 event imply that interplate coupling was weak over the seamount. A large rupture area with small slip occurred in front of the seamount. Its northern bound could be determined by a trace of multiple subducted seamounts. Whereas a subducted seamount itself may not define the rupture area, its width may be influenced by that of the seamount.

[1] Nitrous oxide (N 2 O) is an important atmospheric greenhouse gas and is involved in stratospheric ozone depletion. Analysis of the isotopomer ratios of N 2 O (i.e., the intramolecular distribution of 15 N within the linear NNO molecule and the conventional N and O isotope ratios) can elucidate the mechanisms of N 2 O production and destruction. We analyzed the isotopomer ratios of dissolved N 2 O at a site in the eastern tropical North Pacific (ETNP) and a site in the Gulf of California (GOC). At these sites, the flux of N 2 O to the atmosphere is extremely high but denitrification activity in the oxygen minimum zone (OMZ) also reduces N 2 O to N 2 . We estimated the isotopomeric enrichment factors for N 2 O reduction by denitrification. The factor was À11.6 ± 1.0% for the bulk (average) N, À19.8 ± 2.3% for the center N (a-site nitrogen), À3.4 ± 0.3% for the end N (b-site nitrogen), and À30.5 ± 3.2% for the 18 O of N 2 O. Isotopomer analysis of N 2 O suggests that nitrifiers should contribute to N 2 O production more than denitrifiers at the oxycline above the OMZs in the ETNP (50-80 m) and in the GOC (80-300 m). In contrast, denitrifiers should largely contribute to the N 2 O production and consumption in the OMZs both in the ETNP (120-130 m) and in the GOC (600-800 m). The N 2 O isotopomer analysis will be a useful tool for resolving the distribution of water masses that carry a signal of N loss by denitrification.