Dissertation Abstract
Dynamic seascapes: a quantitative framework for scaling pelagic ecology and biogeochemistry
Kavanaugh, Maria T 2012 http://www.whoi.edu/hpb/Site.do?id=15073
College of Oceanic and Atmospheric Sciences, Oregon State University (United States), 201 pp.
Our understanding of marine pelagic microbial responses and feedbacks to climate change is hampered by the lack of a framework by which to link local mechanism to large scale patterns. The scaling of open ocean observations must address the ubiquitous patchiness of the environment, a dynamic advective medium that challenges the tracking of coherent patches through time, and limited historical context due to the relative rarity and constraints of ship-based sampling. Where terrestrial ecology draws from rich natural history and landscape theory to address issues of scale and boundaries, the pelagic seascape concept is still in its infancy.
We have applied the patch mosaic paradigm of landscape ecology to the study of the spatial, seasonal and interannual variability of the North Pacific in order to facilitate comparative analysis between pelagic ecosystems and provide spatiotemporal context for eulerian time-series studies. Using a multi year record of multivariate remote sensing observations, we classified hierarchical seascapes at monthly and interannual scales. These dynamic, objectively-determined seascapes offer improved hydrographic coherence compared to oceanic regions with static, subjectively-defined boundaries and represent unique biogeochemical functioning and microbial communities. Furthermore they connect satellite studies and in situ observations and allow for objective comparison of ecosystem forcing.
The extent and boundaries of pelagic seascapes change in response to both seasonal and large-scale climatic forcing. On a seasonal scale, distinct nutrient and primary productivity regimes derived from in situ observations were well-characterized, with seascapes also revealing regional forcing of pCO2 and resulting in 33 % reduction in error of an empirical predictive model (from 18.5 µatm to 12.0 µatm pCO2). Surface microbial community structure, as determined by flow cytometry, was different across seasonal seascapes with the strength and forcing of the assemblage by environmental factors varying among seascapes. In the subtropics, interannual shifts in the position of seascape boundaries contribute to the variability observed at the benchmark time series Station ALOHA, with increased in situ phytoplankton abundance (as measured by chl-a), net primary productivity, and relative abundance of eukaryotic phytoplankton observed during periods of encroachment by a seascape corresponding to the transition between subtropical and subarctic environments. While the areal extent of the entire subtropics oscillates, the dynamic range (~6 million km2) of subtropical expansion from 1998-2010 is derived almost entirely by a reduction in the extent of the transition seascape. On interannual time scales, this may result in a transfer of ~1.2 Pg of total annual primary production between the subtropical and the transition ecosystem; while the former is dominated by an efficient microbial loop with episodic events of organic matter export to the deep ocean, the transition ecosystem is an important atmospheric carbon sink primed for recurring export.
This dissertation provides a first step to characterize the seascape variability in the NE Pacific and to understand the modulation of primary and export production in a critical transition region. The multivariate seascape approach described here provides spatiotemporal context for in situ studies and allows objective comparisons of systems’ responses to climate forcing.
We have applied the patch mosaic paradigm of landscape ecology to the study of the spatial, seasonal and interannual variability of the North Pacific in order to facilitate comparative analysis between pelagic ecosystems and provide spatiotemporal context for eulerian time-series studies. Using a multi year record of multivariate remote sensing observations, we classified hierarchical seascapes at monthly and interannual scales. These dynamic, objectively-determined seascapes offer improved hydrographic coherence compared to oceanic regions with static, subjectively-defined boundaries and represent unique biogeochemical functioning and microbial communities. Furthermore they connect satellite studies and in situ observations and allow for objective comparison of ecosystem forcing.
The extent and boundaries of pelagic seascapes change in response to both seasonal and large-scale climatic forcing. On a seasonal scale, distinct nutrient and primary productivity regimes derived from in situ observations were well-characterized, with seascapes also revealing regional forcing of pCO2 and resulting in 33 % reduction in error of an empirical predictive model (from 18.5 µatm to 12.0 µatm pCO2). Surface microbial community structure, as determined by flow cytometry, was different across seasonal seascapes with the strength and forcing of the assemblage by environmental factors varying among seascapes. In the subtropics, interannual shifts in the position of seascape boundaries contribute to the variability observed at the benchmark time series Station ALOHA, with increased in situ phytoplankton abundance (as measured by chl-a), net primary productivity, and relative abundance of eukaryotic phytoplankton observed during periods of encroachment by a seascape corresponding to the transition between subtropical and subarctic environments. While the areal extent of the entire subtropics oscillates, the dynamic range (~6 million km2) of subtropical expansion from 1998-2010 is derived almost entirely by a reduction in the extent of the transition seascape. On interannual time scales, this may result in a transfer of ~1.2 Pg of total annual primary production between the subtropical and the transition ecosystem; while the former is dominated by an efficient microbial loop with episodic events of organic matter export to the deep ocean, the transition ecosystem is an important atmospheric carbon sink primed for recurring export.
This dissertation provides a first step to characterize the seascape variability in the NE Pacific and to understand the modulation of primary and export production in a critical transition region. The multivariate seascape approach described here provides spatiotemporal context for in situ studies and allows objective comparisons of systems’ responses to climate forcing.