Masahiko Fujii

Assessment of skill and portability in regional marine biogeochemical models: Role of multiple planktonic groups

[1] Application of biogeochemical models to the study of marine ecosystems is pervasive, yet objective quantification of these models’ performance is rare. Here, 12 lower trophic level models of varying complexity are objectively assessed in two distinct regions (equatorial Pacific and Arabian Sea). Each model was run within an identical onedimensional physical framework. A consistent variational adjoint implementation assimilating chlorophyll-a, nitrate, export, and primary productivity was applied and the same metrics were used to assess model skill. Experiments were performed in which data were assimilated from each site individually and from both sites simultaneously. A cross-validation experiment was also conducted whereby data were assimilated from one site and the resulting optimal parameters were used to generate a simulation for the second site. When a single pelagic regime is considered, the simplest models fit the data as well as those with multiple phytoplankton functional groups. However, those with multiple phytoplankton functional groups produced lower misfits when the models are required to simulate both regimes using identical parameter values. The cross-validation experiments revealed that as long as only a few key biogeochemical parameters were optimized, the models with greater phytoplankton complexity were generally more portable. Furthermore, models with multiple zooplankton compartments did not necessarily outperform models with single zooplankton compartments, even when zooplankton biomass data are assimilated. Finally, even when different models produced similar least squares model-data misfits, they often did so via very different element flow pathways, highlighting the need for more comprehensive data sets that uniquely constrain these pathways.

A one-dimensional ecosystem model applied to time-series Station KNOT

A vertically one-dimensional ecosystem model is applied to Station KNOT (Kyodo North Pacific Ocean Time series; 44°N, 155°E). This model has 15 compartments, including two categories of phytoplankton (diatoms and non-diatom small phytoplankton) and three categories of zooplankton (small, large and predatory zooplankton). Observed seasonal cycles of ecosystem dynamics at Station KNOT, such as surface nutrient concentrations and column-integrated chlorophyll-a, are successfully reproduced by the model. Observed significant seasonality of a total primary production is also reproduced, but its amount is overestimated by more than 50%, especially during summer. The simulated spring diatom bloom seems to occur 1 month earlier than in reality, considering dramatic decreases in the observed surface silicate in May and June, but it is impossible to determine the time of the actual bloom more precisely because of lack of data in April. Sensitivity studies for several important parameters are described. The Ekman upwelling velocity strongly affects the amount of the total primary production. Stoichiometry of silicon to nitrogen for diatoms strongly determines the amount of the primary production by small phytoplankton. Maximum photosynthetic rate for diatoms contributes to set both the timing and strength of the spring diatom bloom. Maximum rate of grazing on diatoms by large zooplankton controls the timing of the end of the spring diatom bloom and the strength of the autumn diatom bloom. While most of the parameters can be set to the same values as those for Station A7 (41.5°N, 145.5°E), in the Northwestern Pacific like Station KNOT, some values need to be modified. The modification of the parameter values may be partly caused by the difference in the ecosystem dynamics between Stations KNOT and A7. Observations of the mixed-layer depth and surface nutrient concentrations in March and April, when they reach their maxima, are strongly required to reduce uncertainty of the parameter values.

An Index to Determine Vulnerability of Communities in a Coastal Zone: A Case Study of Baler, Aurora, Philippines

A coastal community vulnerability index (CCVI) was constructed to evaluate the vulnerability of coastal communities (Buhangin, Pingit, Reserva, Sabang, and Zabali) in the municipality of Baler, Aurora, Philippines. This index was composed of weighted averages of seven vulnerability factors namely geographical, economic and livelihood, food security, environmental, policy and institutional, demographic, and capital good. Factor values were computed based on scores that described range of conditions that influence communities’ susceptibility to hazard effects. Among the factors evaluated, economic and livelihood, policy and institutional and food security contributed to CCVI across communities. Only small variations on CCVI values (i.e., 0.47–0.53) were observed as factor values cancelled out one another during combination process. Overall, Sabang received the highest CCVI, which was contributed mainly by geographical and demographic factors. This technique to determine factors that influenced communities’ vulnerability can provide information for local governments in enhancing policies on risk mitigation and adaptation.

A spatiotemporal approach for determining disaster-risk potential based on damage consequences of multiple hazard events

Natural hazards have become increasingly frequent in the Philippines, making the determination of risks associated with large-scale natural hazards and disasters in this area increasingly important. This study developed a method for estimating the risk of disasters from multiple hazards in this country at the province level. The locational probability and consequences of five natural hazards were analyzed over a 30-year period (1982–2011), and the disaster-risk potential of provinces was estimated based on the combined damage cost per capita from five hazards over that period. Information from the Center for Research on the Epidemiology of Disasters Emergency Disasters Database (CRED-EMDAT) was used to analyze the areas and populations affected, damage costs, and frequency and duration of five hazards (i.e. meteorological, climatological, hydrological, geophysical, and biological). The estimated values were then presented spatially using a geographic information system. The results suggested that meteorological hazards were the most common hazards affecting most provinces in the Philippines, whereas hydrological hazards produced the most damage. Small island provinces and coastal zones were among the areas with the highest disaster-risk potential. This assessment can aid in decision making with regard to financing disaster prevention schemes and in planning for the increasing occurrences of natural hazard-related disasters.

Projecting the impacts of rising seawater temperatures on the distribution of seaweeds around Japan under multiple climate change scenarios.

Seaweed beds play a key role in providing essential habitats and energy to coastal areas, with enhancements in productivity and biodiversity and benefits to human societies. However, the spatial extent of seaweed beds around Japan has decreased due to coastal reclamation, water quality changes, rising water temperatures, and heavy grazing by herbivores. Using monthly mean sea surface temperature (SST) data from 1960 to 2099 and SST-based indices, we quantitatively evaluated the effects of warming seawater on the spatial extent of suitable versus unsuitable habitats for temperate seaweed Ecklonia cava, which is predominantly found in southern Japanese waters. SST data were generated using the most recent multiple climate projection models and emission scenarios (the Representative Concentration Pathways or RCPs) used in the Coupled Model Intercomparison Project phase 5 (CMIP5). In addition, grazing by Siganus fuscescens, an herbivorous fish, was evaluated under the four RCP simulations. Our results suggest that continued warming may drive a poleward shift in the distribution of E. cava, with large differences depending on the climate scenario. For the lowest emission scenario (RCP2.6), most existing E. cava populations would not be impacted by seawater warming directly but would be adversely affected by intensified year-round grazing. For the highest emission scenario (RCP8.5), previously suitable habitats throughout coastal Japan would become untenable for E. cava by the 2090s, due to both high-temperature stress and intensified grazing. Our projections highlight the importance of not only mitigating regional warming due to climate change, but also protecting E. cava from herbivores to conserve suitable habitats on the Japanese coast.

An improved estimation of the poleward expansion of coral habitats based on the inter-annual variation of sea surface temperatures

The poleward expansion of coral habitats has been observed along the Japanese coast since the 1930s. Previous modeling studies have projected a poleward expansion using decadal-mean sea surface temperatures (SSTs) in the coldest months. However, this poleward expansion could be affected by the inter-annual variation of SST in the coldest months, which has not been considered before. In this study, the simulated pattern of poleward expansion was compared between cases where coral mortality was considered based on the inter-annual variation of SST and the decadal-mean SST in the coldest months. Modeled monthly mean SSTs for historical and future global warming simulations from the most recent climate projection model (MIROC4h) were used. The poleward expansion of corals simulated by considering mortality based on the inter-annual variation of SST in the coldest months better reproduced the observed poleward expansion speed compared to the simulations without such a consideration. Our results show the importance of considering coral mortality based on the inter-annual variation of seawater temperature to produce a more realistic poleward expansion of coral habitats.

Roles of Physical Processes in the Carbon Cycle Using a Simplified Physical Model

A simplified physical model is proposed in this article to describe differences among basins in substance distributions which were not well described by previous simplified models. In the proposed model, the global ocean is divided into the Pacific/Indian Ocean (PI), the Atlantic Ocean (AT), the Southern Ocean and the Greenland/Iceland/Norwegian Sea. The model is consisted of five physical parameters, namely the air-sea gas exchange, the thermohaline circulation, the horizontal and vertical diffusions, and the deep convection in the high-latitude regions. Individual values of these parameters are chosen by optimizing model distribution of natural 14C as a physical tracer. The optimal value for a coefficient of vertical diffusion in the low-latitude region is 7.5 × 10−5 [m2s−1]. Vertical transports by the Antarctic Bottom Water and the North Atlantic Deep Water are estimated at 1.0 Sv and 9.0 Sv. Global-mean air-sea gas exchange time is calculated at 9.0 years. Using these optimal values, vertical profiles of dissolved inorganic carbon without biological production in PI and AT are estimated. Oceanic responses to anthropogenic fluctuations in substance concentrations in the atmosphere induced by the industrialization and nuclear bomb are also discribed, i.e., the effects appear significantly in AT while a signal is extremely weak in PI. A time-delay term is effective to make the PI water older near the bottom boundary.

Development of a Large-Scale, Long-Term Coral Cover and Disturbance Database in the Philippines

The Philippines is located in the tropics and contains highly diverse coral reefs, as it lies within the Coral Triangle, which is the global center of marine biodiversity. However, this biodiversity “hotspot” has experienced reef degradation driven by natural disturbances and intense anthropogenic pressures. Consequently, coral researchers are focusing on promoting awareness of local reefs through the conservation, management, and assessment of reefs to monitor coral health. The status of coral reefs in the Philippines has been reported periodically since surveys were initiated in the 1970s. This study presents the preliminary steps to develop a large-scale, long-term coral cover database in the Philippines. The research was conducted through personal communications and electronic search of coral studies by different sectors (government, nongovernmental organizations, and reef scientists) conducted all over the Philippines. The collated data consist of living hard coral cover percentages from 2,349 reef benthic surveys conducted between 1978 and 2010. These data were analyzed to assess the spatial and temporal variability of Philippine reefs and to determine recent trends in coral cover. Overall, the results revealed an increase in areas with low levels ( 75 %) of coral cover. The results indicated that the Visayan Sea area is at high risk, with the highest ratio of sites with low levels of cover across time periods. Based on a review of the disturbances driving the reef decline, anthropogenic impacts are the most prevalent threat to Philippine reefs.

Potential Future Coral Habitats Around Japan Depend Strongly on Anthropogenic CO2 Emissions

Using the results from the NCAR CSM1.4-coupled global carbon cycle–climate model under the Intergovernmental Panel on Climate Change (IPCC) emission scenarios SRES A2 and B1, we estimated the effects of both global warming and ocean acidification on the future habitats of corals in the seas around Japan during this century. As shown by Yara et al. (Biogeosciences 9:4955–4968, 2012), under the high-CO2-emission scenario (SRES A2), coral habitats will be sandwiched and narrowed between the northern region, where the saturation state of the carbonate mineral aragonite (Ωarag) decreases, and the southern region, where coral bleaching occurs. We found that under the low-emission scenario SRES B1, the coral habitats will also shrink in the northern region by the reduced Ωarag but to a lesser extent than under SRES A2, and in contrast to SRES A2, no bleaching will occur in the southern region. Therefore, coral habitats in the southern region are expected to be largely unaffected by ocean acidification or surface warming under the low-emission scenario. Our results show that potential future coral habitats depend strongly on CO2 emissions and emphasize the importance of reducing CO2 emissions to prevent negative impacts on coral habitats.

Habitat-forming seaweeds in Japan (fucoids and temperate kelps)

This paper describes the flora of habitat-forming seaweeds (fucoids and temperate kelps) at 7673 sites of the Japanese coast encompassing its warm to cold temperate zone, recorded from 1887 to 2014. The data set includes 86 species (21,168 presence and 20,845 absence records), compiled from 355 literature sources, most of which were written in Japanese and published as grey literature in local journals or individual reports. Scientific names were consolidated under currently-accepted nomenclature based on Algaebase (http://www.algaebase.org). The data set compiled the seaweed flora at each study site each year, the geographical location and the scientific names. Additionally, three supporting data sets were created respectively including name of each site, synonyms of the seaweeds, and the corresponding literature list. This rich collection of data can be used to study the biogeography and long-term changes of particular species and the diversity of habitat-forming seaweeds of the Japanese coast.