Guest post by David Middleton, feature image borrowed from iHerb.
A rapid loss of phytoplankton threatens to turn the western Indian Ocean into an “ecological desert,” a new study warns. The research reveals that phytoplankton populations in the region fell an alarming 30 percent over the last 16 years.
The source of this latest “oh no!” is this paper:
Among the tropical oceans, the western Indian Ocean hosts one of the largest concentrations of marine phytoplankton blooms in summer. Interestingly, this is also the region with the largest warming trend in sea surface temperatures in the tropics during the past century—although the contribution of such a large warming to productivity changes has remained ambiguous. Earlier studies had described the western Indian Ocean as a region with the largest increase in phytoplankton during the recent decades. On the contrary, the current study points out an alarming decrease of up to 20% in phytoplankton in this region over the past six decades. We find that these trends in chlorophyll are driven by enhanced ocean stratification due to rapid warming in the Indian Ocean, which suppresses nutrient mixing from subsurface layers. Future climate projections suggest that the Indian Ocean will continue to warm, driving this productive region into an ecological desert.
After reviewing the SI and the blog post, I have to ask, “Is Chris Mooney doing peer review for the AGU?”
The authors present no evidence of phytoplankton decline or any actual measurements of phytoplankton…
Observed Data. Though marine primary production can be assessed directly using field flux measurements, chlorophyll pigment concentration measured through satellites is used as a convenient indicator of phytoplankton biomass and extent, as it represents the magnitude and variance in marine primary production and captures the first order changes in phytoplankton biomass [Ryther and Yentsch, 1957]. These satellite observations, which are mostly based on the visible bands of the radiance spectra (412-555 nm), lack consistent and accurate measurements of surface chlorophyll whenever cloudy conditions persist, which of course, is an integral part of the Asian summer monsoon season. Though seasonal and monthly mean composites can be derived from satellite data to some extent, it is challenging to derive robust signals of long-term trends of chlorophyll over the Indian Ocean because the current availability of satellite data is limited to a fairly short period since the satellite era [Boyce et al., 2010; Rykaczewski and Dunne, 2011]. Studies suggest that the number of years required to detect a trend above the natural variability in most of the global oceans is 50-60 years, though a shorter period of 20-30 years could be used to extract the trends in the tropical oceans including the western Indian Ocean [Beaulieu et al., 2013; Henson et al., 2010]. The recently available satellite data blended from the multiple sensors of satellites bring the number of years of continuous data up to 16 years, bringing it close to the required trend detection time.
The chlorophyll data is obtained from version 2 of the European Space Agency’s Ocean Color-Climate Change Initiative (OC-CCI) [Sathyendranath et al., 2016]. The OC-CCI uses processors for atmospheric correction and retrieval of in-water properties on the basis of round-robin comparison of candidate algorithms [Brewin et al., 2015; Müller et al., 2015]. The OC-CCI chlorophyll product is generated from merged normalized remote-sensing reflectances from SeaWiFS, MODIS-Aqua, and MERIS satellites at 4 km-by-4 km horizontal resolution, band shifted to SeaWiFS wavebands. The POLYMER algorithm used by OC-CCI for processing MERIS data [Steinmetz et al., 2011] is able to retrieve usable data under sun-glint conditions, which improves the coverage in the Arabian Sea, especially during the summer monsoons. The OC-CCI data is available for the period 1998-2013. However, the last couple of years (2012 and 2013) suffer from data gaps (less than 50% coverage) in the Arabian Sea, which could introduce spurious trends. These two years are presented in the analysis for an overview, but are not utilized for estimating the trends and correlation coefficients in the current analysis.
They have a model relating certain satellite imagery to oceanic chlorophyll content and relating chlorophyll to phytoplankton primary production. Their historical climate data are generally based on models simulations. Without any actual data, they clam that they found “an alarming decrease of up to 20% in phytoplankton in this region over the past six decades.”
Previous work actually measuring phytoplankton primary productivity in the region indicate that it is increasing.
The lead author posted this on an AGU blog…
21 JANUARY 2016
Rapid warming over the Indian Ocean reduces marine productivity
Posted by nbompey
By Roxy Mathew Koll
Roxy Mathew Koll is a climate scientist at the Indian Institute of Tropical Meteorology in Pune, India, and lead author of the new study, “A reduction in marine primary productivity driven by rapid warming over the tropical Indian Ocean” that was recently published online in Geophysical Research Letters.
Increasing water temperatures in the Indian Ocean are taking a toll on the marine ecosystem, according to our new study.
Almost 90 percent of the extra heat generated by increased greenhouse gases in the atmosphere has been absorbed by the oceans. Among tropical oceans, ocean warming is most prominent in the Indian Ocean. Now, a new study by me and my colleagues suggests rapid warming in the Indian Ocean reduced marine phytoplankton up to 20 percent during the past six decades.
Such a decline in the marine phytoplankton may cascade through the food chain, potentially turning this biologically productive region into an ecological desert. It may also impact food security in the Indian Ocean rim countries and also the global fisheries market.
The blog post featured three maps.
The first one indicates that marine phytoplankton are booming in the Indian Ocean:
Marine phytoplankton in the tropical oceans 1998 to 2007. Red indicates large concentrations. From Behrenfeld et al., 2006.
Credit: American Geophysical Union
The second is of sea surface temperature trends from 1950-2012:
Surface warming in the tropical oceans 1950 to 2012. Red indicates strong warming.
Credit: American Geophysical Union
These two maps demonstrate no decline in Indian Ocean phytoplankton productivity nor any correlation between warming and productivity.
The third map and the basis of their absurd claim is of chorophyll trends…
Trend in marine phytoplankton in the Indian Ocean 1950 to 2012. Purple indicates a significant decline.
Credit: American Geophysical Union
Anyone with eyeballs can see that the areas of chlorophyll decline correlate to the areas that haven’t warmed…