| || || Nandini, Sri Durgesh|
| || || Projected seasonality in ocean acidification in the Western Pacific |
Author:Nandini, Sri Durgesh
Institution: University of the South Pacific.
Subject: Ocean acidification -- Oceania
Call No.: pac TD 427 .A27 N36 2012
Copyright:10-20% of this thesis may be copied without the authors written permission
Abstract: Oceans play a vital role in mitigating the rate of climate change by uptake of atmospheric CO2, thus altering the seawater chemistry. The pH and aragonite saturation state (Ωar) are reduced, collectively known as ocean acidification. Aragonite is a form of calcium carbonate utilized by most reef building corals. Previous studies indicate that coral growth (calcification) rates typically decline as saturation states decrease. This reduction impacts the resilience of coral reefs to respond to environmental pressures. Consequently, island nations such as those in the tropical Western Pacific, which rely on coral reefs, may be adversely impacted. Aragonite saturation states are projected to continue declining as the oceans continue to take up atmospheric CO2. In this study, we investigate how the seasonal and long-term Ωar and its key drivers change under the high (A2) and control atmospheric CO2 emission scenarios. We focus on the Pacific region (35°S: 30°N; 120°E: 220°E), and the subregions of the West Pacific Warm Pool (WPWP) and the East Equatorial Pacific (EEQ). Most relevant to this thesis is the evaluation of the Community Climate System Model (CCSM3) ocean carbon model against upper ocean seasonal data for this region. Generated seasonal model-data residuals, time-space correlation, root mean square error, and seasonal Taylor Diagrams are used to assess the simulated mean monthly temporal and spatial patterns, seasonal cycle amplitude and phase for the next 100 years. The model-observed estimates give a correlation (R) of 0.85 with mean seasonal surface Ωar values drop from 3.8 to 2.3 by 2100. The mean seasonal amplitude in Ωar decreases by 4% while the seasonal phase remains unchanged till 2100. As Ωar decreases by 2100, the relative seasonal variability becomes larger at the tropics, with Total Carbon Dioxide (TCO2) being the main driver for the entire region as well as subregions. However, at the WPWP there is a strong cancellation effect due to dilution (caused by intensified hydrological cycle by 2100) being the main driver and at the EEQ seasonal upwelling drives the TCO2, suggesting that future levels of atmospheric CO2 will determine the value of Ωar (acidification). Model predictions mentioned have a high degree of uncertainty associated with future precipitation in this region. Despite the model biases mentioned, there is confidence in this model for capturing changes over the next 100 years since we see robust results.