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• 1. [Article] Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison

  This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for ...

  Citation × Citation Citation Abstract Copy Title: Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison Author: Alder, Jay R. This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for the Last Glacial Maximum, deglacial, and Holocene time periods. The model output is evaluated against the best available proxy reconstructions in a detailed data-model comparison. ENSO strength is analyzed in seven paleo simulations and compared to coral and laminated lake sediment proxy records to provide an understanding of how ENSO related mechanisms varied in the past and how they vary under increased atmospheric CO₂ forced global warming. The GENMOM simulated present-day is found to be on par with three models used in the IPCC AR4 assessment and is comparable with reanalysis products (e.g, NCEP2). Atmospheric features such as the jet stream structure and major semipermanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. Most ocean surface currents are reproduced except where they are not resolvable at T31 resolution. Overall, GENMOM captures the observed gradients and spatial distributions of annual surface temperature and precipitation and the simulations are on par with other AOGCMs. Deficiencies in the GENMOM present-day simulation include a warm bias in the surface temperature over the southern oceans, a split in the ITCZ and weaker-thanobserved overturning circulation. GENMOM produces a global temperature bias of 0.6 °C. GENMOM is demonstrated to capture ENSO dynamics similar to eight AOGCMs that were evaluated in the IPCC AR4. The Niño 3 - 4 indices have a standard deviation within 0.3 °C of the observations, indicating GENMOM is producing variability in the tropical Pacifc that is comparable to observations. GENMOM produces present-day ENSO events with an average period of 5.6 years, which is within the 2 – 7 range exhibited in the observed historical record. The mid-Holocene (6ka) and Last Glacial Maximum (LGM, 21ka) simulations are compared to the best available proxy reconstructions for sea surface temperature, precipitation and net moisture to ensure the simulations are plausible. This thesis finds that the model is in good agreement over broad spatial scales, with regional discrepancies between the model and proxy data. Coral and laminated lake sediment proxy records indicate mid-Holocene ENSO strength was reduced by 15 - 60%, offering a scenario in which ENSO-related components can be tested in climates different than present-day, thereby providing context for future changes in ENSO. The mid-Holocene simulations exhibit a 20% reduction of ENSO strength, caused by a precession forced enhancement of the Indian summer monsoon, which strengthened ENSO-related Bjerknes feedbacks. ENSO strength in the LGM is weakened by ~25%, which is not found to be caused by changes in equatorial Pacific dynamics but rather mean state cooling that weakens the tropical thermocline. The 2x and 4x simulations have strongly enhanced and more frequent ENSO events caused by disproportionate warming of the eastern Pacific relative to the western Pacific, which weakens the east-west Pacific surface temperature gradient, allowing larger anomalies, and hence ENSO events, to develop. Title: Simulating past, present, and future changes in ENSO : a model evaluation and data-model comparison Author: Alder, Jay R. This thesis presents the results of a formal evaluation of a new AOGCM, GENMOM, demonstrating its ability to simulate present-day climate and ENSO dynamics. The model is applied to simulate climate for the Last Glacial Maximum, deglacial, and Holocene time periods. The model output is evaluated against the best available proxy reconstructions in a detailed data-model comparison. ENSO strength is analyzed in seven paleo simulations and compared to coral and laminated lake sediment proxy records to provide an understanding of how ENSO related mechanisms varied in the past and how they vary under increased atmospheric CO₂ forced global warming. The GENMOM simulated present-day is found to be on par with three models used in the IPCC AR4 assessment and is comparable with reanalysis products (e.g, NCEP2). Atmospheric features such as the jet stream structure and major semipermanent sea level pressure centers are well simulated as is the mean planetary-scale wind structure that is needed to produce the correct position of stormtracks. Most ocean surface currents are reproduced except where they are not resolvable at T31 resolution. Overall, GENMOM captures the observed gradients and spatial distributions of annual surface temperature and precipitation and the simulations are on par with other AOGCMs. Deficiencies in the GENMOM present-day simulation include a warm bias in the surface temperature over the southern oceans, a split in the ITCZ and weaker-thanobserved overturning circulation. GENMOM produces a global temperature bias of 0.6 °C. GENMOM is demonstrated to capture ENSO dynamics similar to eight AOGCMs that were evaluated in the IPCC AR4. The Niño 3 - 4 indices have a standard deviation within 0.3 °C of the observations, indicating GENMOM is producing variability in the tropical Pacifc that is comparable to observations. GENMOM produces present-day ENSO events with an average period of 5.6 years, which is within the 2 – 7 range exhibited in the observed historical record. The mid-Holocene (6ka) and Last Glacial Maximum (LGM, 21ka) simulations are compared to the best available proxy reconstructions for sea surface temperature, precipitation and net moisture to ensure the simulations are plausible. This thesis finds that the model is in good agreement over broad spatial scales, with regional discrepancies between the model and proxy data. Coral and laminated lake sediment proxy records indicate mid-Holocene ENSO strength was reduced by 15 - 60%, offering a scenario in which ENSO-related components can be tested in climates different than present-day, thereby providing context for future changes in ENSO. The mid-Holocene simulations exhibit a 20% reduction of ENSO strength, caused by a precession forced enhancement of the Indian summer monsoon, which strengthened ENSO-related Bjerknes feedbacks. ENSO strength in the LGM is weakened by ~25%, which is not found to be caused by changes in equatorial Pacific dynamics but rather mean state cooling that weakens the tropical thermocline. The 2x and 4x simulations have strongly enhanced and more frequent ENSO events caused by disproportionate warming of the eastern Pacific relative to the western Pacific, which weakens the east-west Pacific surface temperature gradient, allowing larger anomalies, and hence ENSO events, to develop. Close

• 2. [Article] The impact of El Niño events on the pelagic food chain in the northern California Current

  To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by John Wiley ...

  Citation × Citation Citation Abstract Copy Title: The impact of El Niño events on the pelagic food chain in the northern California Current Author: Rykaczewski, Ryan R., Peterson, William T., Fisher, Jennifer L. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by John Wiley & Sons, Ltd. and can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-2486 Title: The impact of El Niño events on the pelagic food chain in the northern California Current Author: Rykaczewski, Ryan R., Peterson, William T., Fisher, Jennifer L. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work. This is the publisher’s final pdf. The published article is copyrighted by John Wiley & Sons, Ltd. and can be found at: http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291365-2486 Close

• 3. [Article] The role of herbivores and productivity on community structure of rocky shores of the Galapagos Islands, Ecuador

  Ecosystems are facing increasing threats from human related activities, such as overfishing, pollution, habitat destruction, species invasions, and diseases, among others. While oceanic islands provide ...

  Citation × Citation Citation Abstract Copy Title: The role of herbivores and productivity on community structure of rocky shores of the Galapagos Islands, Ecuador Author: Vinueza, Luis R. Ecosystems are facing increasing threats from human related activities, such as overfishing, pollution, habitat destruction, species invasions, and diseases, among others. While oceanic islands provide natural laboratories to understand ecological and evolutionary process, they are also particularly vulnerable to these impacts, given their usual isolation from the mainland and the typically high endemism of their flora and fauna. However, we still lack a general understanding of how marine systems in the Galapagos Islands will be affected by multiple human impacts, more severe environmental perturbations and warmer oceans. Rocky shores have been a prime example for the advancement of ecological theories and for the creation of important concepts to support management decisions and conservation actions, such as the predation hypothesis, the keystone species concept and the development of environmental stress models. However, the majority of this knowledge comes from studies conducted at higher latitudes. While most attention in the tropics has been focused on coral reefs and mangroves, other habitats such as rocky shores have remained largely unexplored. The upwelling ecosystems of the Galapagos Archipelago constitute an ideal model where likely consequences of interactions between global climate change and human impacts (e.g. exploitation) can be studied. In particular, variation in ocean upwelling and downwelling conditions (Palacios 2004) associated with seasonal and interannual variability and large scale oceanic-atmospheric perturbations such as ENSO cycles with its warm El Niño (~cessation of upwelling conditions) and cold La Niña (~abnormal upwelling) phase (Chavez et al. 1999). Thus, the Galapagos situation offers a scenario whereby I can assess the interaction among nutrient supply, herbivory and abiotic fluctuations. I used this dynamic system to evaluate the influence of bottom up and top down effects on rocky shore communities. In Chapter 2 I evaluated the role of consumers at different levels of productivity. I manipulated four levels of herbivory, from no macro-herbivores to all herbivores present, combinations of all together, mostly fish, crabs, crabs and including marine iguanas, crabs, sea turtles and fish. I demonstrated that at sites of low productivity herbivores had consistent effects on community structure by reducing the abundance of erect macroalgae which decreased macroalgal and sessile invertebrate's species richness, diversity and evenness. In areas of mid and high productivity the role of consumers was affected by seasonal effects and by warm and cold phases of El Niño Southern Oscillation. In Chapter 3 I evaluated the interactive effect of consumers on species richness, diversity and evenness of primary producers and discussed the results in the context of prevailing top down views on the regulation of marine tropical communities. I further discuss the importance to manage both top down and bottom up factors to maintain ecosystem structure and function at tropical locations. In chapter 4 I used resource and consumer-stress models to predict the outcome of plant animal interactions. I observed how the impact of herbivory on primary producers was exacerbated by thermal stress and reduced algal biomass at times of low productivity and high temperature; this pattern shifted as productivity increased and thermal stress relaxed, which led to herbivores increasing, not decreasing algal biomass. Finally, chapter 5 provides the main conclusions about our work. I put our work in context of past and present ecological theories. I also offer a framework to manage this system, oriented to increasing the resistance and resilience of this fragile ecosystem. Title: The role of herbivores and productivity on community structure of rocky shores of the Galapagos Islands, Ecuador Author: Vinueza, Luis R. Ecosystems are facing increasing threats from human related activities, such as overfishing, pollution, habitat destruction, species invasions, and diseases, among others. While oceanic islands provide natural laboratories to understand ecological and evolutionary process, they are also particularly vulnerable to these impacts, given their usual isolation from the mainland and the typically high endemism of their flora and fauna. However, we still lack a general understanding of how marine systems in the Galapagos Islands will be affected by multiple human impacts, more severe environmental perturbations and warmer oceans. Rocky shores have been a prime example for the advancement of ecological theories and for the creation of important concepts to support management decisions and conservation actions, such as the predation hypothesis, the keystone species concept and the development of environmental stress models. However, the majority of this knowledge comes from studies conducted at higher latitudes. While most attention in the tropics has been focused on coral reefs and mangroves, other habitats such as rocky shores have remained largely unexplored. The upwelling ecosystems of the Galapagos Archipelago constitute an ideal model where likely consequences of interactions between global climate change and human impacts (e.g. exploitation) can be studied. In particular, variation in ocean upwelling and downwelling conditions (Palacios 2004) associated with seasonal and interannual variability and large scale oceanic-atmospheric perturbations such as ENSO cycles with its warm El Niño (~cessation of upwelling conditions) and cold La Niña (~abnormal upwelling) phase (Chavez et al. 1999). Thus, the Galapagos situation offers a scenario whereby I can assess the interaction among nutrient supply, herbivory and abiotic fluctuations. I used this dynamic system to evaluate the influence of bottom up and top down effects on rocky shore communities. In Chapter 2 I evaluated the role of consumers at different levels of productivity. I manipulated four levels of herbivory, from no macro-herbivores to all herbivores present, combinations of all together, mostly fish, crabs, crabs and including marine iguanas, crabs, sea turtles and fish. I demonstrated that at sites of low productivity herbivores had consistent effects on community structure by reducing the abundance of erect macroalgae which decreased macroalgal and sessile invertebrate's species richness, diversity and evenness. In areas of mid and high productivity the role of consumers was affected by seasonal effects and by warm and cold phases of El Niño Southern Oscillation. In Chapter 3 I evaluated the interactive effect of consumers on species richness, diversity and evenness of primary producers and discussed the results in the context of prevailing top down views on the regulation of marine tropical communities. I further discuss the importance to manage both top down and bottom up factors to maintain ecosystem structure and function at tropical locations. In chapter 4 I used resource and consumer-stress models to predict the outcome of plant animal interactions. I observed how the impact of herbivory on primary producers was exacerbated by thermal stress and reduced algal biomass at times of low productivity and high temperature; this pattern shifted as productivity increased and thermal stress relaxed, which led to herbivores increasing, not decreasing algal biomass. Finally, chapter 5 provides the main conclusions about our work. I put our work in context of past and present ecological theories. I also offer a framework to manage this system, oriented to increasing the resistance and resilience of this fragile ecosystem. Close