@unpublished{lester24,
  author = {},
  title = {A model of near-sea ice phytoplankton blooms},
  note = {https://doi.org/10.31223/X5HD7V},
  doi = {10.31223},
  file = {lester24.pdf}
}

Arctic spring blooms of phytoplankton mark the annual emergence of the region’s ecosystem from winter dormancy. Satellite observations show that these blooms have increased in size and magnitude in recent years. While this may be expected to be a result of generally warmer conditions, it has been found that near-ice blooms are spatially correlated with cold and fresh surface water signatures from sea ice melt over hundreds of kilometers. This study develops an idealized model that describes how the environmental impact of meltwater may control the spread of phytoplankton spring blooms in the region. The results support the idea that melt-induced stratification of the surface ocean is a dominant driver of recent changes in near-ice bloom characteristics in the Arctic. This furthermore implies that future changes in sea ice cover under continued Arctic warming will have important consequences for the timing and spread of such blooms.

@article{mcnamara2024policy,
  title = {Policy and market forces delay real estate price declines on the US coast},
  author = {McNamara, Dylan E and Smith, Martin D and Williams, Zachary and Gopalakrishnan, Sathya and Landry, Craig E},
  journal = {Nature Communications},
  volume = {15},
  number = {1},
  pages = {2209},
  year = {2024},
  publisher = {Nature Publishing Group UK London},
  doi = {10.1038/s41467-024-46548-6},
  file = {McNamara24.pdf}
}

Despite increasing risks from sea-level rise (SLR) and storms, US coastal communities continue to attract relatively high-income residents, and coastal property values continue to rise. To understand this seeming paradox and explore policy responses, we develop the Coastal Home Ownership Model (C-HOM) and analyze the long-term evolution of coastal real estate markets. C-HOM incorporates changing physical attributes of the coast, economic values of these attributes, and dynamic risks associated with storms and flooding. Resident owners, renters, and non-resident investors jointly determine coastal property values and the policy choices that influence the physical evolution of the coast. In the coupled system, we find that subsidies for coastal management, such as beach nourishment, tax advantages for high-income property owners, and stable or increasing property values outside the coastal zone all dampen the effects of SLR on coastal property values. The effects, however, are temporary and only delay precipitous declines as total inundation approaches. By removing subsidies, prices would more accurately reflect risks from SLR but also trigger more coastal gentrification, as relatively high-income owners enter the market and self-finance nourishment. Our results suggest a policy tradeoff between slowing demographic transitions in coastal communities and allowing property markets to adjust smoothly to risks from climate change.

@article{mcnamara2023human,
  title = {Human--coastal coupled systems: Ten questions},
  author = {McNamara, Dylan E and Lazarus, Eli D and Goldstein, Evan B},
  journal = {Cambridge Prisms: Coastal Futures},
  volume = {1},
  pages = {e20},
  year = {2023},
  publisher = {Cambridge University Press},
  doi = {10.1017/cft.2023.8},
  file = {human-coastal-coupled-systems-ten-questions.pdf}
}

Given the inevitability of sea-level rise, investigating processes of human-altered coastlines at the intermediate timescales of years to decades can sometimes feel like an exercise in futility. Returning to the big picture and long view of feedbacks, emergent dynamics, and wider context, here we offer 10 existential questions for research into human–coastal coupled systems.

@article{sandin2022evidence,
  title = {Evidence of Biological Self-Organization in Spatial Patterns of a Common Tropical Alga},
  author = {Sandin, Stuart A and Edwards, Clinton B and Zgliczynski, Brian J and Pedersen, Nicole E and Smith, Jennifer E and McNamara, Dylan E},
  journal = {The American Naturalist},
  volume = {200},
  number = {5},
  pages = {722--729},
  year = {2022},
  publisher = {The University of Chicago Press Chicago, IL},
  doi = {10.1086/721323},
  file = {Sandin22.pdf}
}

Tropical reef communities contain spatial patterns at multiple scales, observable from microscope and satellite alike. Many of the smaller-scale patterns are generated physiologically (e.g., skeletal structures of corals at <1-m scale), while some of the larger patterns have been attributed to scale-dependent feedbacks (e.g., spur and groove reefs at 10–100-m scales). In describing the spatial patterning of reef benthic communities at landscape levels, we uncovered unique spatial patterning among living marine algae. Populations of the calcifying green alga Halimeda were observed to form a consistent polygonal pattern at a characteristic scale of 3–4 m. The pattern showed no clear evidence of having been formed through biologically created shifts in hydrodynamical conditions or related mechanisms. In considering the specifics of Halimeda growth patterns, a model of self-organization involving separation and patterned extension is proposed, a mechanism revealed in some geological pattern formation. This observation reinforces the diversity of pathways by which striking spatial patterns can occur in ecosystems.

@article{williams2021variations,
  title = {Variations in stability revealed by temporal asymmetries in contraction of phase space flow},
  author = {Williams, Zachary C and McNamara, Dylan E},
  journal = {Scientific Reports},
  volume = {11},
  number = {1},
  pages = {5730},
  year = {2021},
  publisher = {Nature Publishing Group UK London},
  doi = {10.1038/s41598-021-84865-8},
  file = {williams_mcnamara_2021.pdf}
}

Empirical diagnosis of stability has received considerable attention, often focused on variance metrics for early warning signals of abrupt system change or delicate techniques measuring Lyapunov spectra. The theoretical foundation for the popular early warning signal approach has been limited to relatively simple system changes such as bifurcating fixed points where variability is extrinsic to the steady state. We offer a novel measurement of stability that applies in wide ranging systems that contain variability in both internal steady state dynamics and in response to external perturbations. Utilizing connections between stability, dissipation, and phase space flow, we show that stability correlates with temporal asymmetry in a measure of phase space flow contraction. Our method is general as it reveals stability variation independent of assumptions about the nature of system variability or attractor shape. After showing efficacy in a variety of model systems, we apply our technique for measuring stability to monthly returns of the S&P 500 index in the time periods surrounding the global stock market crash of October 1987. Market stability is shown to be higher in the several years preceding and subsequent to the 1987 market crash. We anticipate our technique will have wide applicability in climate, ecological, financial, and social systems where stability is a pressing concern.

@inproceedings{mcnamara2018barrier,
  title = {Barrier islands as coupled human--landscape systems},
  author = {McNamara, Dylan E and Lazarus, Eli D},
  journal = {Barrier dynamics and response to changing climate},
  pages = {363--383},
  year = {2018},
  publisher = {Springer}
}

In recent decades, coastal development has transformed barrier systems around the world. The longest, most intensively developed chain of barriers extends along the Atlantic and Gulf Coasts of the U.S., where mean population density is the highest in the country. There are nearly 300 barrier islands between Maine and Texas, and of these, at least 70 are intensively built-up. Concentrated development exists and continues despite the fact that barrier islands are transient landscapes, not only over geologic time scales of millennia, but also within human and economic time scales of centuries to decades. Populated barrier islands are inherently vulnerable to natural hazards such as sea-level rise, cumulative erosion, and storm events; this vulnerability drives humans to actively modify barrier geometry and environments. The most common manipulations are beach nourishment, to mitigate shoreline erosion, and increases to dune height or seawall construction to prevent flooding and damage from overwash during storm events. Over time scales of years to decades, hazard-mitigation actions impact natural, spatio-temporal barrier processes such as washover deposition and planform transgression, which in turn affect future efforts to manage, control, or prevent changes to barrier morphology. Through their maintenance and persistence, interventions against coastal hazards represent a significant dynamical component of developed barrier-island system evolution, such that, within the past century, human actions and natural barrier-island processes have become dynamically coupled. This coupling leads to steady-state barrier-island behaviors that are new. A fundamental way to understand how developed barrier islands will respond to climate change over decadal time scales is to treat these settings as strongly coupled human–natural systems. Dynamical demonstration of coupled-system behavior suggests new avenues for less reactionary and more holistic coastal management perspectives for barrier systems and raises questions about whether and how society may adapt to coastal change. Over time scales longer than centuries, human interventions may be coupled only weakly to long-term barrier dynamics. Short of major technological advancements or sweeping decisions to transform these environments into comprehensively geoengineered terrains, high-density development on U.S. barrier islands will eventually have to change—perhaps radically—from its current configuration.