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Last update: 22 December 2005

ECRP-seminar titles and abstracts 2005

Decemnber 22 (Thu), 2005

Tomomichi KATO, Mitsuru HIROTA, Yanhong TANG, Xiaoyong CUI, Yingnian LI, Xingquan ZHAO, Takehisa OIKAWA

Strong temperature dependence and no moss photosynthesis in winter CO2 flux for a Kobresia meadow on the Qinghai-Tibetan Plateau

We examined the CO2 exchange of a Kobresia meadow ecosystem on the Qinghai-Tibetan Plateau using a chamber system. CO2 efflux from the ecosystem was strongly dependence on soil surface temperature. The CO2 efflux-temperature relationship was identical under both light and dark conditions, indicating that no photosynthesis could be detected under light conditions during the measurement period. The temperature sensitivity (Q10) of the CO2 efflux showed a marked transition around -1.0C; Q10 was 2.14 at soil surface temperatures above and equal to -1.0C but was 15.3 at temperatures below -1.0C. Our findings suggest that soil surface temperature was the major factor controlling winter CO2 flux for the alpine meadow ecosystem and that freeze-thaw cycles at the soil surface layer play an important role in the temperature dependence of winter CO2 flux.

Michio J. Kishi

Fish growth comparisons around Japan using NEMURO.FISH

NEMURO.FISH has been applied to saury and herring, we applied the same kinds of bioenergetics model coupled with NEMURO, to common squid and chum salmon. Squid and chum salmon migrate from spawning area to nursery area by grazing zooplankton, the concentration of which was calculated by NEMURO. The results show good agreement with body weights of those fish/squid, and can explain the role of temperature, food density on their growth.

November 24 (Thu), 2005: Special Seminor

Takehito Yoshida (Cornell University, Ecology & Evolutionary Biology)

Toward the understanding of complex population dynamics: is evolution a matter for ecology?

Ecologists have long been interested in understanding population dynamics in nature. Although theoretical ecologists have shown that mathematical models can represent various dynamical behaviors and empirical ecologists have confirmed that some types of dynamics actually exist in nature, we do not yet completely understand how population dynamics are driven. The list of possible mechanisms driving population dynamics is still growing. We have been trying to understand population dynamics of a planktonic predator-prey (rotifers-algae) system cultured in a laboratory microcosm. Although laboratory microcosms are indeed different from real ecological systems, understanding laboratory model systems can provide new insights into real systems. Rapid evolution is one of the previously unexplored mechanisms that we found can dramatically change the ecological dynamics of a predator-prey system. There is a genetic variability within our algal population, and algal genotypes (clones) exhibit an evolutionary tradeoff between defense against rotifer grazing and competitive ability for nutrient. In response to changes in grazing pressure and nutrient concentration, different algal genotypes are expected to change their frequencies. We are now trying to directly track the evolutionary changes using a new genetic technique. We also bring this "evolution" idea over to a study of "clear water phase", which is a cyclic behavior of seasonal dynamics often found in natural lakes and ponds. Finally, I will discuss how "rapid" evolutionary change can be compared to ecological change, using some published data from natural systems.

Relating publications 1. Yoshida T, Jones LE, Ellner SP, Fussmann GF, Hairston NGJr. (2003) Rapid evolution drives ecological dynamics in a predator-prey system. Nature 424:303-306
2. Yoshida T, Ellner SP, Hairston NGJr. (2004) Evolutionary tradeoff between defense against grazing and competitive ability in a simple unicellular alga, Chlorella vulgaris. Proceeding of the Royal Society of London Series B-Biological Sciences 271:1947-1953
3. Yoshida T. (2005) Toward the understanding of complex population dynamics: planktonic community as a model system. Ecological Research 20: 511-518
4. Hairston NGJr, Ellner SP, Geber MA, Yoshida T, Fox JA (2005) Rapid evolution and the convergence of ecological and evolutionary time. Ecology Letters 8: 1114-1127
5. Fussmann GF, Ellner SP, Hairston NGJr, Jones LE, Shertzer KW, Yoshida T. (2005) Ecological and evolutionary dynamics of experimental plankton communities. Advances in Ecological Research 37: 221-243

November 24 (Thu), 2005


Climate regime shifts and lower trophic level phenology in the western North Pacific

Since the start of the Ecosystem Change Research Program of the FRCGC in FY2000, we have been conducting a series of retrospective studies based on the historically collected observational data sets after the 1960s in the several domains of the western North Pacific. This presentation is to summarize the regional comparison of the lower trophic level responses to the decadal scale climatic forcing in the western North Pacific. As there is a growing recognition on importance of functional/taxonomic breakdown of biological processes for better understanding of mechanisms and consequences of the ecosystem changes, we have particularly focused on the plankton community structure rather than merely looking at the bulk biomass. One of our major findings was alternation of seasonal phytoplankton and zooplankton communities which roughly coincided with the climatic regime shifts in 1976/77 and 1988/89. Those indicated phenological changes in the lower trophic levels. Both in the light-limited subarctic and nutrients-limited subtropical regions, spring bloom season seemed to start later than usual after the mid 1970s although the average timing of the beginning of bloom differed between the regions. During the same years, the blooming season seemed to end earlier due to strong stratification. Winter time cooling coupled with rapid summertime warming might be responsible for the delayed initiation and the early termination of productive season. In the 1990s, on the contrary, warm winter and cool summer elongated the annual productive season. The majority of the past climate-ecosystem link studies have emphasized winter to spring processes. However, our study suggested that climatic forcing with a different decadal scale cycle worked in winter and summer to present seasonal and interannual variation of hydrographic conditions, and thus combination of such the wintertime and summertime processes determined the seasonal/interannual biological productivity.


Successional replacement mediated by frequency and severity of wind and snow disturbances in a Picea-Abies forest

Effects of wind and snow disturbances on the successional replacement of Picea glehnii by Abies sachalinensis were investigated in a subalpine coniferous forest of cool temperate northern Japan. Tree demography (growth, mortality and recruitment rates) was determined by repeated measurements of stem diameter and height, and multiple censuses in four Picea-Abies stands undergoing succession. Aboveground stand biomass, residence time and tree growth trajectories of the component species were estimated to examine successional changes in structure and dynamics. Individual-based simulations were used to examine the effects of disturbances that slowed succession. Multiple regression analyses were used to determine the relative importance of disturbance frequency and intensity on species composition during succession. Aboveground biomass was larger in P. glehnii than in A. sachalinensis stands, whereas residence time, a proxy of productivity, was much shorter for A. sachalinensis than for P. glehnii populations. During successional replacement, both species increased in initial growth rate and decreased in size-dependency of growth in canopy gaps. These plastic growth responses were more prominent in P. glehnii than in A. sachalinensis. Disturbance frequency was the most important predictor of species composition in the simulations, and windstorms were more important than snowfall in terms of disturbance intensity. The frequency of natural disturbances does not have the potential to initiate stand dynamics; however, it slows succession. When disturbance is locally frequent because of the direction and pitch of the topography, early-successional P. glehnii stands may persist for thousands of years.
Accepted by the Journal of Vegetation Science in November 2005.

October 20 (Thu), 2005

Remote sensing of biomass and spring phenology in boreal regions, and integration in a Dynamic Vegetation Model

I will present my works concerning the remote sensing of spring phenology and biomass, and the collaboration with Sheffield Dynamic Global Vegetation Model team.

Variations in spring phenology, taken as the date at which the tree leaves appear, reflect climatic variations. Phenology also influences the annual exchanges of carbon dioxyde between the vegetation and the atmosphere. Remote sensing methodologies were developed to measure the spring phenology in the boreal regions, were snow influences strongly the radiometric signal. The RMS error in phenological dates is 6 to 9 days, with no bias. These measurements were used to (1) analyse the temporal variations in phenology between 1982 and 2004, (2) develop a phenology modele based on temperature, (3) which was then integrated in the Sheffield Dynamic Global Vegetation Model.

A methodology to measure forest biomass using the L-band Synthetic Aperture Radar onboard the ongoing ALOS satellite was developed. Such radar systems can measure biomass upto 50 tons/ha, allowing to monitor regenerating forests. Biomass estimates from remote sensing were used to identify areas uncorrectly modeled by the Sheffield Dynamic Global Vegetation Model.

Yoshikawa, C., M. Kawamiya and T. Kato

Results of the C4MIP Phase 2 experiments using KISSME

We have conducted global warming experiments for the C4MIP (Coupled Carbon Cycle Climate Model Intercomparison Project) Phase 2 (experiments with full coupled model) with KISSME which is an A&OGCM included marine and terrestrial carbon cycle models. The model was forced by anthropogenic emission of CO2 for the 1850-2100 time period. We performed simulations with and without interactions between climate and carbon cycle. By the end of the 21th century the difference in atmospheric CO2 concentration caused by the warming was only 20ppm in the last result unlike the other C4MIP model results. This is because the soil carbon storage was too small. As a result of improvements of terrestrial carbon cycle model, the difference became about 120ppm which is close to the majority value of the C4MIP models.

September 15 (Thu), 2005

Reiichiro ISHII

Plant community structure transitions induced by sensitive "supporting actors"

The structures and components of plant communities are not determined by their own species specific abilities (resource acquisition, dispersal...) alone, but also by their interactions with pollinators, dispersers, grazers and so on. With examples from my previous studies, I show that qualitative (sometime abrupt) transitions of plant community structures could be induced by the changes in pollination and herbivory regimes. If they are more short-lived and more fugitive and more sensitive to a given environmental change than their hosts, they might alter plant communities, thereby the ecosystem-functions faster than expected.

Hisashi SATO, Akihiko ITOH, and Takashi KOHYAMA

Recent progress in the SEIB-DGVM, and future plans

The SEIB-DGVM is a dynamic ecological model, which aims to simulate transient impacts of climatic change on terrestrial ecosystem, and land-atmosphere interactions. It contains mechanical-based or empirical-based algorithms for (1) Land physical processes, (2) Plant physiological processes, and (3) Plant dynamic processes. By now, first version of the model is developed, and the first paper is going to be submitted. In this seminar, I will talk about recent progresses of the SEIB-DGVM showing latest results. I will also talk about our future plans of our model, namely (1) connect SEIB-DGVM to the integrated-earth-system-model of the kyousei2 project, and (2) employ more sophisticated way for scaling up.

July 21 (Thu), 2005

Rikie Suzuki (ECRP), Jianqing Xu, and Ken Motoya (HCRP)

Global analyses of satellite-derived vegetation index related to climatological wetness and warmth

Wetness and warmth are the principal factors that control global vegetation distribution. This paper investigates climate-vegetation relationships at a global scale using the normalized difference vegetation index (NDVI), warmth index (WAI), and wetness index (WEI).

The NDVI was derived from a global, 20-year Advanced Very High Resolution Radiometer (AVHRR) dataset with 4-minute resolution. The WEI was defined as the ratio of precipitation to potential evaporation. The WAI was defined as the cumulative monthly mean temperature that exceeds 5C annually. Meteorological data from the International Satellite Land-Surface Climatology Project Initiative II (ISLSCP II) dataset were used to calculate the WEI and WAI. All analyses used annual values based on averages from 1986 to 1995 at 1 x 1 degree resolution over land. Relationships among NDVI, WEI, and WAI values were examined using a vegetation-climate diagram with the WEI and WAI as orthogonal coordinates.

The diagram shows that large NDVI values correspond to areas of tropical and temperate forests and large WEI and WAI values. Small WEI and WAI values are associated with small NDVI values that correspond to desert and tundra, respectively.

Two major regimes are revealed by the NDVI vegetation-climate diagram: wetness dominant and warmth dominant. Wetness dominates mid- and low latitudes. Warmth dominates high latitudes north of 60N or elevated land such as the Tibetan Plateau. The boundary between the two regimes roughly corresponds to the vegetation boundary between taiga forest and southern vegetation. Over northern Eurasia, the boundary occurs in areas where the NDVI is large and the maximum monthly temperature is around 18C.

S. Lan Smith

Quantitatively Comparing Photo-acclimation Models for Phytoplankton

First, I will briefly describe the key features of photo-acclimation models and their recent development. To illustrate the kinds of changes these models aim to simulate, I will present observations from several laboratory incubation studies. Developers of a few different models have simulated these same observations. I will focus on two models and (mostly) and one set of observations simulated by the developers of both. The author of the more recent model claims to better simulate these observations. Indeed, he was able to begin his simulation from the start of the experiment, whereas the author of the older model began his simulation 5 days into the experiment. The author of the newer model claims to be able to simulate the "initial lag" in phytoplankton growth. Indeed, there are good reasons why this sounds convincing. However, neither study applied any mathematical method (data assimilation) to fit its model to the observations. Each presented only a "hand-tuned" simulation, and they appear to simulate the observations comparably well (except for the initial lag). To quantitatively compare the models, I have begun fitting each model to the observations (from the start of the experiment). I will present preliminary results and reasons why the newer model is better for large-scale simulations.

June 9 (Thu), 2005


Effect of artificial nitrogen load on soil respiration and methane adsorption in cool-temperate forest in Japan.

Since it has been pointed out in the early 1970s that the acidification of rain reduce productivity in northern European forests, many studies on effects of acid rain on the forest ecosystems have been vigorously carried out in the world. Direct effects of acid rain on trees and plants in the forest ecosystems were investigated at the beginning of the studies. Recent studies are, however, being focused on indirect effects on the soil ecosystems, especially effects of increase in nitrogen deposition (NO3-concentration in rain) on the ecosystems. Therefore, the present study is focused on effects of artificial nitrogen load on CO2 and CH4 fluxes from soil in three experimental sites (a broad-leaved deciduous forest with Sasa community, a broad-leaved deciduous forest without Sasa community and a coniferous forest).

Yoshikazu SASAI

Ventilation process in the North Pacific using CFCs distributions

May 19 (Thu), 2005

Akihiko ITO

Modeling of carbon cycle and fire regime in an East Siberian larch forest

Biomass burning by wildfire is an important component of ecosystem dynamics and carbon cycle. In this study, a coupled carbon cycle and fire regime model was developed and applied to a larch forest in East Siberia, one of the fire-prone ecosystems. The model is composed of a 10-compartment carbon cycle scheme and a grid-based stochastic fire regime scheme, in which carbon budget and fire behaviors are simulated interactively. I will present a brief introduction, model description, and several results, as well as a short slideshow of larch forest.


Toward ecosystem modeling in the equatorial Pacific Ocean
- OCMIP3 model and a regional model -

In the equatorial Pacific Ocean, the easterly trade winds create persistent equatorial upwelling. Nitrate upwelled into the euphotic zone in the equatorial Pacific region accounts for about one-fifth of the global estimate. Equatorial upwelling also brings up subsurface water with relatively high concentrations of total inorganic carbon, which results in the outgassing of carbon dioxide, making the equatorial Pacific the largest natural source of CO2 to the atmosphere. Preliminary results in the equatorial Pacific from the numerical models for the OCMIP (The Ocean-Carbon Cycle Model Intercomparison Project) will be presented. Although there are reasonable agreements in interannual variations of surface pressure of CO2 and surface flux among the models, the time mean distributions show some varieties; some models show much higher nutrient concentrations than observation. To investigate how low nutrient condition is maintained in the equatorial region, a simple ecosystem model coupled with a regional circulation model is under development. The plan and progress will be reported.

April 21 (Thu), 2005


Temporal and spatial variability of chlorophyll-a and primary productivity in the sub-arctic North Pacific using multi-sensor remote sensing

The sub-arctic north Pacific represents one of the most biologically productive regions in the world ocean. Nutrient concentrations in deep waters are the highest in the global ocean because it is the terminal region for the abyssal circulation. High primary productivity and strong air-sea interactions characterize the carbon cycle of this region. Biogeochemical processes in the ocean play an important role in environmental changes. These processes are affected by the biological pump; hence, monitoring the variability of the distribution of chlorophyll a (chl-a) and primary productivity is very important to understand oceanic biogeochemical cycles.

To describe and understand the processes controlling the temporal and spatial variability of chlorophyll-a (Chl-a) and primary productivity (PP) in the sub-arctic north Pacific during 1997 to 2000, we examined seasonal and interannual variabilities of the distributions of chl-a and PP utilizing a combination of satellite remote sensing data from ocean color (OCTS and SeaWiFS), sea surface temperature (SST, AVHRR), wind speed (SSM/I) and photosynthetically available radiation (PAR, SeaWiFS), as well as climatology data. Time series data of primary productivity on a monthly time scale were computed using the VGPM (Beherenfeld and Falkowski, 1997). The inputs to the VGPM are satellite-derived surface chl-a, SST, and PAR at the water surface. To help understanding the regulatory mechanism of chl-a and primary productivity distributions, calculation was made for sea surface nitrate using SST and chl-a satellite data (Goes et al,. 1999,2000).

Ocean color imagery clearly showed seasonal and interannual variability in the spatial abundance and distribution of chl-a in this study area. Satellite data helped discern several features, most importantly the existence of significant east-west gradients in the supply of nitrate in winter, in the consumption of nitrate by phytoplankton and in phytoplankton production and biomass accumulation over the growth season. Multiple regression analysis of time-series data showed that over 65% of the variations in PP in the sub-arctic Pacific could be explained solely on the basis of changes in the strength of sea surface winds and the intensity of incident irradiance (PAR). The dependence of PP on sea surface wind stress was far greater in the western sub-arctic Pacific Gyre (WSG), than in the Alaskan Gyre (ALG) due to diminishing impact of surface winds towards the east. Spring accumulation of phytoplankton biomass was greater in the WSG than in the ALG despite the higher rates of PP in the latter. In addition, large interannual variations in phytoplankton biomass and PP were observed in the sub-arctic Pacific following the onset of the El-Nino event of 1997 and the transition to La-Nina conditions in 1999. These variations were largely the result of differences in meteorological and oceanographic conditions across the sub-arctic Pacific following the development of the El-Nino.

Hideki Kobayashi

Simulation of the spectral light environment in the forest canopy using atmosphere-vegetation radiative transfer model

Recent increase in atmospheric aerosols alters the radiation regimes both in atmosphere and vegetation. Major changes in radiation regimes are reduction in total solar radiation and increase in a fraction of diffuse radiation, and change in spectral composition of radiation. These changes in radiation would change the forest canopy photosynthesis activity through the change in available photon flux above the canopy and under the forest floor. Especially in East and Southeast Asia, these influences can be more serious in the near future owing to the heavy aerosol loading in the atmosphere. To evaluate this influence more precisely, I have developed three-dimensional forest canopy radiative transfer model using Monte Carlo technique. In the model, the forest canopy and the stem are modeled as cone and cylinder shape, respectively. Forest floor grasses are modeled as a plane parallel layer. Minimum scattering and absorption media are leave that are uniformly distributed in the cone shaped and plane parallel objects. In this seminar, initial results of the spectral light environment are introduced with a special emphasis on the forest floor condition.

March 24 (Thu), 2005

Tomomichi KATO

Development of the coupled climate-terrestrial carbon cycle model

Interactions between the climate and the terrestrial carbon cycle have the potential to provide major feedbacks on climate change, but major uncertainties in the magnitude of these feedbacks persists. To clarify those uncertainties, the terrestrial ecosystem carbon cycle model, Sim-CYCLE, is combined with the CCSR/NIES/FRCGC AGCM5.7b (including a land surface model: MATSIRO). The Sim-CYCLE derives the climate data from the AGCM and gives the LAI, CO2 concentration and Net Carbon Budget (net ecosystem production minus carbon emission due to the land use change) to the AGCM through the coupler in the MATSIRO. Now we have almost accomplished the attachment cording of the Sim-CYCLE to MATSIRO-AGCM under the Kyousei-2 project. That combined model shows a reasonable distribution of the LAI, NPP and other carbon storages in the 1000yrs spin-up run. This seminar introduces the preliminary results of the coupled run in 20th century.

Michio J. KISHI(1,3), Yukiko ONO(1), and Takeshi OKUNISHI(2)

1 Graduate School of Fisheries Sciences, Hokkaido University
2 Graduate School of Engineering, Hokkaido University
3 Frontier Research Center for Global Change

A lower trophic ecosystem model of Okhotsk Sea including iron effect

Ecosystem model including iron effects is constructed in the Okhotsk Sea. The model includes phytoplankton, zooplankoton, NO3-N, PON, DON and four kinds of iron categories, i.e., 1 iron from aerosol, 2 iron from Amur River, 3 iron from bottom mud and 4 iron from biological compartments. POM (Princeton Ocean Model) is used as a physical model and KKYS (Kawamiya et al., 1995) was used as a basic ecosystem model. High Nutrient Low Chl-a (HNLC) are clearly identified in the model with iron effect in the Northwestern Pacific. However iron effect is too strong in the Okhotsk Sea. The biological parameters should be tuned.

January 17 (Thu), 2005


Will salps rule the Antarctic Ocean?: mesoscale physical-biological coupling study

This talk is not a part of my current research topic in FRCGC but to introduce what I had studies for my PhD thesis. Antarctic marine ecosystem had been believed as a diatom-krill (Nankyoku-Okiami)-based simple, stable and thus effective system. However, this "old dogma" has been changing as biologists started recognizing importance of zooplankton other than krill, copepods and salps, Based on the samples collected for 1988 - 1996 by Japanese and Australian Ice Breakers, I investigated environmental factors which caused the spatio-temporal shift of key-stone plankton species from krill to others. Different from krill and copepods, I found that salps favored a warmer, oligotrophic condition which were likely to be presented by meandering of the Antarctic Circumpolar Current and extensive sea ice retreat.

Recent reports on occasional salp blooms and decrease in krill catch suggest that decrease in the Antarctic sea ice area associated with global warming trend might seriously damage the higher trophic level animals, such as marine mammals and sea birds, which depend on krill as major food resources.

Dennis DYE

Toward an Improved PAR Data Set for Global Carbon Cycle Modeling

Process models of terrestial ecosystem-atmosphere CO2 exchange and primary production typically require data on the flux of photosynthetically active radiation (PAR, 400-700 nm) at the Earth's surface. Existing data sources for PAR are limited and generally inadequate with regard to spatial coverage, resolution, and the separation of diffuse and beam flux components. This seminar will introduce a remote sensing-based strategy for developing an improved global PAR data set that addresses these inadequacies. The modeling strategy involves fusion of data on atmospheric properties (clouds, aerosols) from multiple satellite sensors (e.g., MODIS Terra/Aqua, MTSAT) with atmospheric radiation transfer modelling to achieve regional-to-global PAR estimates at high spatial and temporal resolution on a near-realtime basis. This planned, new data source is expected to contribute to improved accuracy in modeling of the contemporary terrestrial (and potentially ocean) carbon cycle. Current research issues and plans will be discussed.

January 27 (Thu), 2005


Factors important for forest stature in northern Japan

Trees grow tall where resources are abundant and stresses are minor. Current hypotheses of height limitation focus on increasing water transport constraints in taller trees. Increasing leaf water stress due to gravity and path length resistance may ultimately limit leaf expansion and photosynthesis for further height growth. Despite abundant water resources, trees taller than 30 m are rarely found in Japanese forests that are frequently subjected to typhoons and heavy snowfall. Mechanical damage may not be a minor factor of height limitation. I studied the relationships between mechanical failure of conifer species and their crown size along the growth trajectory. Changing probability of mechanical damage along tree growth was positively associated with crown dimensions, but was not associated with the stem slenderness ratio and modulus of elasticity. For confer species and under conditions of frequent loading, crown shape emerged as the most important predictor of mechanical damage, and maximum height was biomechanically determined.

S. Lan Smith (FRCGC), Beatriz E. Casareto (Laboratory of Aquatic Science Consulting Co., Tokyo), Mohan P. Niraula (Shizuoka University), Yoshimi Suzuki (Shizuoka University), James D. Annan (FRCGC), Julia C. Hargreaves (FRCGC), and Yasuhiro Yamanaka (FRCGC)

Examining the Regeneration of Nitrogen by Assimilating Data from Incubations into a Multi-element Ecosystem Model

We examined the flows of nitrogen in a pair of batch incubations of plankton assemblages under controlled conditions, using mesopelagic seawater from different depths. Observations included concentrations of nutrients, organic matter (particulate and dissolved) and plankton (biomass by species). Because nitrogen flows were not observed directly, we examined them using a multi-element ecosystem model developed to simulate these experiments. Dynamic changes in the observed bulk POC:PON ratio (C:N ratio of particulate organic matter, POM) were consistent with a quota model of the flexible composition of phytoplankton. To relate these changes to the regeneration of nitrogen, we included such a quota model and all major planktonic groups observed.

By assimilating the data (all observations of carbon and nitrogen concentrations, including living carbon biomasses) into the model, we accurately simulated the changes in bulk POC:PON ratio and its difference between incubations. We examined the simulated flows of nitrogen, dividing the ecosystem between the Microbial Food Web (MFW) and Grazing Food Web (GFW) based on sizes of organisms. The MFW dominated the regeneration of nitrogen in both incubations. After nitrate depletion, gross nitrogen regeneration varied inversely with observed POC:PON ratio. Our results suggest that bulk POC:PON ratio could also be used to constrain the regeneration of nitrogen in models of the oligotrophic ocean.

* I will also describe my recent work revising a paper describing this work and re-running the assimilations to prepare a re-submission of this work for publication. This entails performing sensitivity analyses and Identical Twin Tests (ITTs) to choose which subset of the model parameters should be varied in the assimilation.

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