Daniela Turk

Satellite ocean-color observations of the tropical Pacific Ocean

The Coastal Zone Color Scanner (CZCS) data set provided some insights into biological processes in the equatorial Pacific, but the sampling was too sparse to address questions on temporal and spatial variability. Since late 1996, the Ocean Color–Temperature Sensor (OCTS), the Polarization Detection Environmental Radiometer (POLDER), the Sea-viewing Wide Field-of-View Sensor (SeaWiFS), and the Moderate-Resolution Imaging Spectroradiometer (MODIS) have provided a nearly continuous record of biological processes in this region for the first time. This study summarizes the SeaWiFS observations of the tropical Pacific from September 1997 through March 2000, with particular emphasis on equatorial and mesoscale variability, the influence of biological processes on penetrating irradiance, and the performance of primary production algorithms in this region. Specific mesoscale phenomena described are the phytoplankton blooms along the west coast of Central America, in the vicinity of the Costa Rica dome, and south of the equator. The coastal Central American and Costa Rica dome blooms result from orographically steered coastal winds and Ekman divergence, respectively. An unusual bloom event occurred south of the equator and persisted for several months in 1999; specific mechanisms that would have sustained the bloom could not be identified. Also, the time-evolution of the equatorial bloom during the May–August 1998 transition from El Ni * no to La Ni * na is discussed. Again, no concise and broadly accepted explanation of the bloom’s genesis and migration has yet emerged. During this transition, the monthly mean diffuse attenuation coefficient decreased by a factor of 3 at some locations along the equator. This change in water transparency, coupled with large changes in mixed-layer depth, resulted in significant changes in surface layer heating rates that were substantiated with field observations. Finally, certain primary production algorithms designed to use remotely sensed chlorophyll-a concentrations are evaluated. None of the algorithms capture the observed variability in primary production, and all appear to underestimate the total primary production of the tropical Pacific. r 2002 Elsevier Science Ltd. All rights reserved.

Geographical distribution of new production in the western/central equatorial Pacific during El Niño and non-El Niño conditions

Rates of new production in the warm waters of the tropical Pacific and their seasonal to interannual variability are estimated by measurement of 15 N-nitrate uptake along the equator in the western and central (145°E-165°W) equatorial Pacific. Measurements were carried out during non-El Nino conditions and two examples of anomalous conditions: the moderate El Nino in 1994-1995 and the strong El Nino in 1997-1998. Variations in new production are explained in relation to changes in physical, chemical, and biological environments during the El Nino-Southern Oscillation cycle. During non-El Nino conditions in the western region the rates of integrated new production over the euphotic zone were low (0.15 mmol m -2 d -1 ) and likely limited by availability of nitrate. In the central region, new production was higher (1.37 mmol m -2 d -1 ) owing to upwelling of nitrate-rich subsurface waters. The east-west asymmetry of observed variables in the western and central equatorial Pacific is altered during El Nino conditions owing to the eastward expansion of the western Pacific Warm Pool. In the western region, during the moderate El Nino in 1994-1995, the integrated new production increased slightly compared to non-El Nino conditions, while during the strong El Nino in 1997-1998, it was higher by a factor of 10 than in non-El Nino conditions. In the central region during the 1994-1995 El Nino, the rates of new production markedly decreased compared to non-El Nino conditions. During the El Nino in 1997-1998, the integrated rates of new production were comparable to non-El Nino conditions, but the vertical distribution showed a downward displacement of maximum rates. The results of our study suggest that interannual variations in new production in the western and central equatorial Pacific correlate well with the change of the nitracline depth during the eastward expansion of the Warm Pool and depend strongly upon the severity of the El Nino event.

Implications of changing El Niño patterns for biological dynamics in the equatorial Pacific Ocean

[1] El Nino events are known to strongly affect biological production and ecosystem structure in the tropical Pacific. Understanding and predicting biological processes in this area are hampered because the existing in situ observing system focuses primarily on physical measurements and does not observe key biological parameters; the only high spatial and temporal resolution biology-related observations are from the global array of ocean color satellites which provide an estimate of surface chlorophyll concentrations only. Since the 1990s, an apparent shift of the El Nino maximum sea-surface temperature (SST) warm anomaly from the eastern to the central equatorial Pacific has frequently been observed. Satellite observations show significant changes in chlorophyll-a (Chl-a), new production (NP) and total primary production (PP) in the equatorial Pacific associated with these new central Pacific (CP) El Nino events (also called El Nino Modoki) relative to eastern Pacific El Ninos. During CP-El Ninos, NP, Chl-a and PP in the central basin are depressed relative to EP-El Ninos and lower values of Chl-a and PP coincide spatially with higher SST in the central Pacific. While surface Chl-a, and integrated NP and PP over the entire equatorial band, decrease during both CP and EP-El Ninos, the magnitude of this decrease seems to depend more on the intensity than type of event. The changing spatial patterns have significant implications for equatorial biological dynamics if, as has been suggested, CP-El Ninos increase in frequency in the future. Citation: Turk, D., C. S. Meinen, D. Antoine, M. J. McPhaden, and M. R. Lewis (2011), Implications of changing El Nino patterns for biological dynamicsinthe equatorial PacificOcean, Geophys. Res. Lett., 38, L23603, doi:10.1029/2011GL049674.

Role of Technology in Ocean Acidification: Monitoring, Water-Quality Impairments, CO 2 Mitigation, and Machine Learning

Ocean acidification (OA), or the reduction in the pH of the ocean, is driven by increasing carbon dioxide concentration in the atmosphere and local pollution. There is already evidence of the detrimental impact of OA on marine organisms. As further increases in atmospheric CO 2 and changes in water quality are expected, it is crucial to develop and implement advanced technologies that enable better monitoring, allow for understanding of adaptation potential of the organisms, and facilitate the use of mitigation strategies toward predicted environmental changes. Collaboration of marine and computer scientists, engineers, and citizens is needed to develop innovative sustainable technologies to mitigate and reduce future increase of CO 2 .

Can Empirical Algorithms Successfully Estimate Aragonite Saturation State in the Subpolar North Atlantic

The aragonite saturation state (ΩAr) in the subpolar North Atlantic was derived using new regional empirical algorithms. These multiple regression algorithms were developed using the bin-averaged GLODAPv2 data of commonly observed oceanographic variables (temperature (T), salinity (S), pressure (P), oxygen (O2), nitrate (NO3-), phosphate (PO4-3), silicate (Si(OH)4), and pH). Five of these variables are also frequently observed using autonomous platforms, which means they are widely available. The algorithms were validated against independent shipboard data from the OVIDE2012 cruise. It was also applied to time series observations of T, S, P and O2 from the K1 mooring (56.5°N, 52.6°W) to reconstruct for the first time the seasonal variability of ΩAr. Our study suggests: (i) linear regression algorithms based on bin-averaged carbonate system data can successfully estimate ΩAr in our study domain over the 0-3500m depth range (R2=0.985, RMSE= 0.044); (ii) that ΩAr also can be adequately estimated from solely non-carbonate observations (R2=0.969, RMSE=0.063) and autonomous sensor variables (R2=0.978, RMSE=0.053). Validation with independent OVIDE2012 data further suggests that (iii) both algorithms, non-carbonate (MEF=0.929) and autonomous sensors (MEF=0.995) have excellent predictive skill over the 0-3500 depth range; (iv) that in deep waters (>500m) observations of T, S and O2 may be sufficient predictors of ΩAr (MEF=0.913); (iv) the importance of adding pH sensors on autonomous platforms in the euphotic and remineralization zone (<500m). Reconstructed ΩAr at Irminger Sea site, and the K1 mooring in Labrador Sea show high seasonal variability at the surface due to biological drawdown of inorganic carbon during the summer, and fairly uniform ΩAr values in the water column during winter convection. Application to time series sites shows the potential for regionally tuned algorithms, but they need to be further compared against ΩAr calculated by conventional means to fully assess their validity and performance.