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Projects

Shedding dynamic light on iron limitation: The interplay of iron limitation and dynamic irradiance conditions in governing the phytoplankton distribution in the Southern Ocean.
The Southern Ocean plays an important role in the global carbon cycle, due to its large size and unique physiochemical characteristics. Approximately 25% of total anthropogenic CO2 uptake by the oceans takes place in the Southern Ocean, mainly via primary production by phytoplankton. However, changes in the Antarctic climate may impact phytoplankton primary productivity and hence the carbon export by the Southern Ocean. Previous experiments in our laboratory have identified taxon-specific differences in photoacclimation to different light conditions that contribute to explaining observed spatial distributions. However, photoacclimation does not seem to be the only factor that controls the phytoplankton distribution, iron demand might play a role as well. Experiments will be conducted on research cruises in the Southern Ocean to test our hypotheses. Data website at: ocean.stanford.edu/dynalife



ICESCAPE - Impacts of Climate change on the Eco-Systems and Chemistry of the Arctic Pacific Environment
ICESCAPE is a multi-year NASA shipborne project. The bulk of the research will take place in the Beaufort and Chukchi Seas in summer of 2010 and fall of 2011. The central science question of this program is, "What is the impact of climate change (natural and anthropogenic) on the biogeochemistry and ecology of the Chukchi and Beaufort seas?" While both of these regions are experiencing significant changes in the ice cover, their biogeochemical response will likely be quite different due to their distinct physical, chemical, and biological differences. Data website at: ocean.stanford.edu/icescape




Iron fertilization of the Southern Ocean: Regional simulation and analysis of C-sequestration in the Ross Sea
A modified version of the dynamic 3-dimensional mesoscale Coupled Ice, Atmosphere, and Ocean model (CIAO) of the Ross Sea ecosystem is being used to simulate the impact of environmental perturbations upon primary production and biogenic CO2 uptake. Three major hypotheses are being tested during the course this study. Hypothesis 1 deals with the degree of iron-cycle complexity required to simulate the dynamics of added iron in surface waters; Hypothesis 2 addresses the most effective iron fertilization strategy given differences in particle flux and export for blooms dominated by different phytoplankton taxa (e.g. diatoms and P. antarctica); Hypothesis 3 is concerned with assessing the degree of feedback between CO2 sequestration and N2O liberation as a result of iron additions.




Photosynthetic characteristics, carbon metabolism, and nutrient requirements of Phaeocystis antarctica and diatoms from the Ross, Sea, Antarctica
Within the Ross Sea, the most productive area of the Southern Ocean, only about two-thirds of the available macronutrients are consumed by phytoplankton prior to the exhaustion of the available iron (Fe). Were more Fe made available, annual production in these waters could be increased by about 50%, depending upon what phytoplankton taxa dominates. One objective of this study is to quantify characteristics of the photophysiology, carbon metabolism, and nutrient acquisition that determines the conditions under which either diatoms or P. antarctica will dominate the phytoplankton population. The second is to determine the potential of each population to act as a sink for atmospheric CO2.



Probing acclimation in Prochlorococcus ecotypes through analyses of global gene expression
Despite its discovery only a little over a decade ago, the prochlorophyte Prochlorococcus marinus has been shown to be very abundant in oligotrophic tropical and subtropical open oceans and among the most productive phytoplankton in the oceanic gyres (accounting for up to 80% of primary production). As such, it is an important component of the marine food web for a significant fraction of the world's oceans. Or primary goal is to determinee the molecular and physiological constraints that set limits on the ability of the different Prochlorococcus



Primary Production and Air-Sea CO2 Exchange in the Northern Polar Seas
Climate in the Arctic is changing faster than anywhere else on the globe. A key question that needs to be addressed is what role the Arctic plays in modulating changing climate and how it will likely respond in the fact of anticipated future changes. The primary objective of this study is to quantify the contribution of Arctic waters to global primary production, and more importantly, to air-sea CO2 exchange. To do so, we will use multi-platform satellite data along with numerical models of primary production to characterize seasonal to interannual changes in rates of primary production and air-sea CO2 exchange within the Arctic Ocean and adjacent northern polar seas. Computed changes in these quantities will be related to dynamics of sea ice cover and the major climate modes (e.g. ENSO, PDO, AO) to gain a better understanding of how C-cycling in Arctic seas are likely to respond to human-induced alterations in global climate.




Global climate change and infectious disease
Our proposed work examines the link between the environment (sea surface temperature), microbial pollution, and the associated risks and rates of illness in coastal waters. Specifically, we will examine physical and biological attributes of coastal systems that result in an observable, understandable, and predictable relationship between sea surface temperature, microbial pollution (i.e. pathogenic and non-pathogenic enteric organisms) along shorelines of urban beaches, and rates of illness. (with Ali Boehm, CEE)



ITR: Computational induction of scientific process models
Despite the relative simplicity of the marine ecosystem in the Ross Sea and the high quality data available for model parameterization and validation, there are still a number of processes that are poorly understood and poorly constrained in the current model. Processes such as zooplankton feeding on phytoplankton can take many functional forms, and it is not clear which is the most suitable for this ecosystem. Not surprisingly, the numeric parameters that these processes would require are also poorly known. The same is true for processes such as sinking of particulate material and conversion of this organic material back into organic forms by bacteria. The space of candidate models is far too great for humans to enumerate systematically. Thus, computational methods for constructing and parameterizing such models are being used to provide valuable insights into which biological processes and coefficients are most compatible with the field data. (with Pat Langley, ISLE)





Modeling UV-B effects on primary production throughout the Southern Ocean using multi-sensor satellite data
We are studying the impact of an Antarctic ozone "hole" event on primary productivity throughout most of the Southern Ocean. This study combines state-of-the-art physiological and bio-optical models of Antarctic primary production with unique Antarctic satellite Data. These satellite data include visible CZCS and SeaWiFS imagery for estimating algal distributions, AVHRR imagery for mapping cloud cover, TOMS data for estimating UVR fluxes, and Special Sensor Microwave Imager (SSM/I) measurements of surface brightness temperature for mapping sea ice concentration. Some of the satellite data is used as input to a radiative transfer model that will calculate UV-A, UV-B, and photosynthetically active radiation (PAR, 400-700 nm) at the Antarctic ocean surface. These radiation fluxes are used to force the bio-optical models, which also take into account the geographic distribution of Antarctic phytoplankton as estimated from the past three decades of oceanographic studies in the Antarctic.



A coupled ice-ocean model of mesoscale physical/biological interactions in the Ross Sea
The primary objective of this research is to understand the principal processes that control the flux of carbon (and related biologically active chemical substances) from surface waters to the deep ocean in the southwestern Ross Sea, the site of the Southern Ocean Joint Global Ocean Flux Study (SOJGOFS). For this a dynamic 3-dimensional model of the coupled sea ice/ice edge/open water ecosystem in the southwestern Ross Sea is being developed to investigate the complex interactions between environmental forcing and the production (primary and secondary) and fate of biogenic carbon which will synthesize observational data collected both in the field (during SOJGOFS and ROAVERRS) and remotely via satellite.



Research on Ocean-Atmosphere Variability and Ecosystem Response in the Ross Sea (ROAVERRS)
ROAVERRS is an interdisciplinary study of meteorologic forcing phenomena, sea ice dynamics, ocean hydrography, primary productivity, and benthic-pelagic coupling in the southwestern Ross Sea, Antarctica. The primary goal is to examine how changes in aspects of the polar climate system, in this case wind and temperature, influence marine productivity on a large Antarctic continental shelf. In the Ross Sea, katabatic winds and mesocyclones influence the spatial and temporal distribution of ice cover as well as upper ocean mixed-layer depth and thus control net primary production in sea ice and open water systems. The standing stock and structure of bottom-dwelling biological communities are also linked to meteorologic processes, owing to intra-seasonal and interannual variation in the horizontal and vertical flux of organic carbon produced in the upper ocean.



The relationship between sea ice and phytoplankton blooms in the western Ross Sea
Satellite data can be an important source of large scale phytoplankton distributions and primary productivity estimates at high latitudes. However, spatial distributions of phytoplankton were relatively unknown until the launch of the Coastal Zone Color Scanner (CZCS) aboard the Nimbus-7 satellite. Since then, substantial phytoplankton blooms in several areas of the Southern Ocean have been reported, often in association with retreating sea ice edges or in coastal polynyas. Unfortunately, the presence of sea ice can present a problem for the interpretation of CZCS imagery at high latitudes. It is crucial, therefore, to determine the extent to which small ice floes are present in highly pigmented Southern Ocean waters. The primary objective of this study is to use RADARSAT SAR data to investigate the relationship between sea ice and phytoplankton distributions in the western Ross Sea.



Remote sensing of phytoplankton production in the Southern Ocean
This project involves high spatial and temporal resolution mapping of sea ice (SSM/I), sea surface temperature (AVHRR), and phytoplankton pigment (SeaWiFS, OCTS/ADEOS, MOS) distributions in the Southern Ocean. The primary objective is to investigate the relationship between mesoscale features (e.g. frontal zones, eddies, marginal ice zone, etc.) which can be observed from space, and rates of primary productivity. To date, few large scale, high resolution studies of the Southern Ocean have been attempted using remote sensing technology, which is unfortunate because in situ sampling in this hostile environment is very difficult and expensive.

Last updated: January 6, 2016