Use of Giovanni

1
James Acker1 Watson Gregg2 Gregory
Leptoukh1 Steven Kempler1 Nancy Casey2 Gene
Feldman3 Charles McClain3 Wayne Esaias2 Suhung
Shen1
Use of Giovanni with Ocean Color Time-Series
Project Data for Trend Detection in the Coastal
Zone
1 NASA Goddard Earth Sciences Data and
Information Services Center (GES
DISC) http//disc.gsfc.nasa.gov/ 2 NASA Goddard
Earth Sciences Division http//earthsciences.gsfc.
nasa.gov/ 3 NASA Ocean Biology
Processing Group http//oceancolor.gsfc.nasa.gov/
Presented at Ocean Optics XVIII, Montreal,
Canada, October 9-13, 2006

Abstract Analysis of Sea-viewing Wide
Field-of-view Sensor (SeaWiFS) chlorophyll
concentration data from 1998 to 2003 indicated an
increasing trend of 4 globally, with the
increase occurring primarily in the coastal zone
(Gregg et al. 2005). As numerous studies exist
which have linked increased fluxes of nutrients
to coastal waters from rivers and estuaries to
higher chlorophyll concentrations and coastal
eutrophication, it is expected that coastal
chlorophyll concentrations will exhibit
increasing trends with variability linked to
precipitation and freshwater flux to the coastal
zone. Acker et al. (2005) employed the GES DISC
Interactive Online Visualization ANd aNalysis
Infrastructure (Giovanni) to observe a strong
chlorophyll response to markedly different flow
conditions at the mouth of Chesapeake Bay in 2002
and 2003. More recent observations have
determined a large chlorophyll concentration
anomaly in November 2005 on the northeast coast
of the United States apparently linked with
near-record autumnal precipitation. In this
study, Giovanni will be used to regionally
characterize chlorophyll concentration trends in
the coastal zone utilizing Ocean Color
Time-Series Project data, and to examine
differences between areas which are influenced by
freshwater flow and areas with minimal influence
of freshwater flow.
CASE STUDIES Several of the regions for which chl
a time-series were generated did not yield a
time-series with statistical significance or a
noteworthy pattern of interest. The case
studies provided here are the most significant
and intriguing examples. The statistical
results and time-series for all 20 regions appear
in the Extended Abstract. (The same color
palette was used for all area maps.)
South America Region 12, Northern Chile Coast
The New England Coastal Chlorophyll Anomaly,
November 2005
In addition to providing the capability to
examine monthly SeaWiFS and MODIS-Aqua chl a
concentration data, Giovanni also provides the
capability of generating chl a concentration
anomalies, which are currently based on a
September 1997-May 2005 base period. This
anomaly analysis capability provided a striking
example of the linkage between terrestrial
hydrology and coastal zone chlorophyll
concentrations on the New England coast in
November 2005.
Region 3 Coastal Japan
This region was chosen to generate a chl a
time-series for a region which clearly exhibited
a statistically significant increasing trend in
the results of Gregg et al. 2005 (see Figure 1).

(Right) Time-series of chlorophyll a
concentration anomalies for the period September
1997 through June 2006 on the New England coast.
The November 2005 anomaly is particularly
evident.
Region 14 Brazil South
While the Coastal Japan time-series is not a
statistically significant trend, the
seasonal peak in monthly chl a concentrations
appears to be generally increasing over the
length of the record.
STUDY METHODOLOGY To examine trends in the
coastal zone, several small regions were selected
where the influence of major river systems was
either expected to be significant, i.e. the
regions were near major river outflow zones, or
regions which were not adjacent to a significant
river system. A few regions were selected to
check on the integrity of the analysis by
comparison to the results of Gregg et al. 2005.
Figure 1 shows the selected regions superimposed
on Figure 1 from Gregg et al. 2005, which
displays areas with positive and negative chl a
trends for the period 1998-2003. Giovanni was
used to create the regional boundaries and to
define the temporal period of analysis. For
each region, a time series of SeaWiFS monthly
data was created for the period January 1998 to
December 2005. Several area plots were created
simultaneously to show the range of chl a in the
region averaged over the full time period.
After the time series was created, the average
monthly values for the designated region were
obtained using the ASCII data output function,
imported to an Excel spreadsheet, and a time
series with linear line fit was generated. The
linear least-squares fit equation describing the
line was generated simultaneously. The average
monthly values were also used to calculate the
statistical significance (P-value) for each time
series (Zar 1976). Giovanni currently utilizes
the Grid Analysis and Display System (GrADS) to
perform its averaging functions. To generate
area average values for a data product over a
specified region, the GrADS function aave is
utilized. aave provides an area-weighted
average for the entire specified region. aave
performs latitudinal weighting by the difference
between the sines of the latitude at the northern
and southern edges of the grid box, and
longitudinal weighting by the interval between
the two adjacent grid points. Missing data values
are not used to calculate the average.
Comparison of chl a concentration anomalies for
November 2004 (left) and November 2005 (right)
on the New England coast.
The Brazil South region covers mostly
oligotrophic waters with very low chl a
concentrations. The time-series nonetheless
displays a slight upward slope. Higher
temporal resolution SeaWiFS 8-day data (right)
shows a clear seasonal pattern and a suggestive
increasing trend in peak seasonal chlorophyll
concentrations.
NCDC precipitation data shows that October 2005
had record precipitation for most states in the
U.S. Northeast. Several localities had
rainfall three times above the monthly average.
Acker et al. 2005 demonstrated that record
rainfall in the Mid-Atlantic in spring 2003
resulted in elevated chl a concentrations at
the mouth of Chesapeake Bay, with a one-
Africa Region 15, Benguela Upwelling Zone
month lag period between maximum freshwater flow
to Chesapeake Bay and peak chl a concentrations
at the mouth of the Bay. The correlation
between record autumnal precipitation in the
Northeast in October 2005 with anomalously high
chl a concentrations in November 2005 indicates
a similar mechanistic linkage between freshwater
flow to the ocean and elevated chl a
concentration.
Summary
Some regions of the Benguela Upwelling Zone were
indicated to have decreasing chl a trends in the
results of Gregg et al. 2005 (Figure 1). These
results are confirmed by the time-series shown
here. The factors contributing to a decrease in
chlorophyll concentration in productive
upwelling zones like the Benguela are of
particular interest in the context of regional
and global climate change.
This study demonstrates the capability of
Giovanni to rapidly provide time series of
chlorophyll a for many different and diverse
regions, establishing baselines for further
investigations with related oceanographic data
sets. Several intriguing patterns are observed
in the time series shown in this study,
particularly declining trends in high
productivity areas both river outflow and
upwelling zones and increasing seasonal peak
concentrations on the coasts of Japan and Brazil.
The time series data that can be generated
rapidly with Giovanni (including improved time
resolution with 8-day data sets) provide vital
information for monitoring regional coastal
changes and trends.
Europe Region 20, Northern Adriatic Sea
References
Acker, J., Harding, L., Leptoukh, G., Zhu, T. and
Shen, S. Remotely-sensed chl a at the Chesapeake
Bay mouth is correlated with annual freshwater
flow to Chesapeake Bay, GEOPHYSICAL RESEARCH
LETTERS, VOL. 32, L056001, doi
10.1029/2004GL021852, 2005. Gregg, W., Casey,
N., and McClain, C. Recent Trends in Global
Ocean Chlorophyll, GEOPHYSICAL RESEARCH LETTERS,
VOL. 32, L03606, doi10.1029/2004GL021808,
2005. Zar, J.H., Biostatistical Analysis, 3rd
Ed., Prentice-Hall, Upper Saddle River, NJ, 1976.
The Northern Adriatic Sea is a region which
receives a significant riverine freshwater input
from the Po River flowing through northern Italy.
Similar to the time-series for the
Mississippi River outflow region, the Northern
Adriatic chl a time-series displays a
statistically significant decreasing trend from
January 1998 through December 2005.
Figure 1. Study area locations (1-20)
superimposed on global map of chlorophyll
concentration trends from Gregg et al. 2005.