/ (Semi -annual Progress Report) 

March 1987 W 

As specified by the contract this is the third progress report concerning 

NAS 5-28769 entitled, "Influence of the Yukon River on the Bering Sea". The 

purpose of this project is to use satellite data to study relationships 

between discharge of the Yukon River to waier-masses and biologic productivity 

in the northern Bering Sea. 

Amended specific ob jecti ves are: 

1. to develop thermal and sediment surface maps using TM data of the 

discharge of the Yukon River and the Alaska Coastal Current during 

the ice free season; 

2. to develop a historical model of the distribution of the Yukon River 

discharge and the Alaska Coastal Current using Landsat MSS and NOAA 

sate1 1 i te imagery; 

to use high resolution TM data to define the surface dynamics of the 

front between the Alaska Coastal Current and the Bering Shelf/Anadyr 

Current; and 

3. 

4. to verify TM and other image analyses with field data - cost to be 

shared with other projects in the area. 

The development of chlorophyll surface maps using the TM data has been 

eliminated as an objective. The western limit of TM data transmission has 

prevented the acquisition of data in areas where chlorophyll concentration is 

high and thus could be analyzed. In the Norton Sound area where TM data has 
been acquired the water is highly turbid masking signatures that would be 

related to chlorophyll production. The presence of high concentrations of 

suspended sediments and low salinity also hinder chlorophyll production in 

that area. However, ISHTAR (Inner Shelf Transfer and Recycling) project 

investigators are measuring the distribution and abundance of chlorophyll in 

the water column and the results will be incorporated in the NASA project. 

The latest efforts for this project have concentrated on image analysis 

of TM data, review of 1986 ship board measurements collected by ISHTAR 

investigators and completion of the inter-annual and intra-annual analysis of 

turbid water. TM data recorded on July 5 and 22 1985 of the Yukon Delta and 

Norton Sound area were analyzed. 

The July 5 data is a night-time pass over the boundary of the Alaska 

Coastal and Bering Shelf water-masses, and the Yukon Delta. The thermal band 

is the only usable channel due to the timing of the pass. Subsections were 

extracted from the data to experiment with digital enhancement techniques that 

will display structures in the water. A fourier-gaussian filtered image (fig. 

1) significantly improved the visual perception of these structures. The data 

is being used to study the mixing of the two water masses. Field measurements 

acquired by ISHTAR investigators and the image data will be used to analyze 

the water-mass boundary. 

The July 22, 1985 TM data is a day-time pass over Norton Sound. A 

subsection was extracted from the data that included turbid Yukon water. 

Several digital techniques were applied to the data to enhance structures and 

boundaries in the turbid water including: piece-wise contrast stretches, a 

variety of color composites, fourier-transform edge-enhancement, band ratios 

and principal components analysis. The color composites, of the first four 

principal components and the ratio of band 1 to 3 best displayed structures in 
the turbid water (fig. 2 & 3). Some of these structures appear to be related 

to factors other than variations in the concentration of suspended 

sediments. 

also be related to the presence of shoals and aquaticvegetation. Field data 

from ISHTAR investigations needed to identify these structures is limited due 

to very shallow waters this close to the delta. 

The structures provide information on flow characteristics and MY 

An ISHTAR sponsored workshop, for investigators studying the Bering Sea 

was held during January in Florida. Tentative results of the remote sensing 

project were presented and compared to ship-board measurements and 

oceanographic models presented by ISATAR and OCSEAP ( Outer Continental She1 f 

Environmental Assessment Program) investigators. As discussed in the previous 

progress report (October 19861, the water masses delineated on the imagery 

correlate with the distribution of nitrate, chlorophyll, water temperatures 

and salinity measured in the water column. 

of the water-column data is very similar to the patterns observed on the 

thermal imagery (fig. 4). The boundaries of the water-masses on the images do 

not precisely correlate with the water column values for several reasons: 

The geometry of the distribution 

the image data records sea surface or near surface values while shipbased measurements are acquired throughout the water column; 

the satellite data is an instantaneous recording of the surface while 

water column measurements are acquired over a 10-15 day time 

interval ; 

water-masses are determined by temperature and sal i ni ty (i .e. 

density) so distribution does not always with temperature 

only; 

/ 
4) the sate1 li te sensor records sea-surface temperatures or reflected 

solar energy while ship-board measurements evaluate different 

parameters such as chlorphyll or nitrate; and 

5) the density-sliced satellite image gives the illusion of a distinct 

solid boundary while in reality it is gradational and dynamic. 

A manuscript entitled, "Distribution and circulation of turbid Yukon 

River water" is in preparation. This paper describes the inter-annual and 

intra-annual analysis of turbid water discharged by the Yukon River based on 

analysis of Landsat MSS data recorded between 1974 and 1978. After further 

revision the manuscript will be submitted to a refereed journal. A copy of 

the preliminary abstract and conclusions are included as Appendix A. An 

abstract has also been written and accepted for the POAC meeting (Appendix B). 

Some Prel imi nary Fi ndi ngs 

The distribution of near-surface, turbid water, discharged by the Yukon 

River, was studied based on analysis of satellite imagery. The interannual 

analyses indicates that the net flow of near-surface, turbid water is 

northward of the delta across the entrance to Norton Sound. Only turbid water 

to the east enters Norton Sound and consists of 25% of the total area based on 

areal measurements. Approximately 10% of that water circulates into the sound 

along the southern coast and is lost to view in the vicinity of Unalakleet. 

Suspended sediments transported by this southern circulation are primarily 

deposited along the southern coast. 

circulate in then out of Norton Sound, possibly resulting in some deposition 

Turbid water to the northeast appears to 

along the northern coast. 

Three distinct zones within the turbid water have been identified based 

on relative brightness levels. These zones appear to be primarily related to 
differences in suspended-sediment concentrations and position of the sediments 

in the water column. Zone one which is adjacent to the delta has the highest 

suspended sediment concentrations, low bioturbation and corresponds to the 

submarine deltaic morphology. 

bioturbation increases in zone two and three, which are successively seaward 

of zone 1. The interannual extent of turbid water and modern Yukon sediments 

on the,sea-bottom are very similar. This similarity is the result’of currents 

located along their boundaries in the Bering Sea and in northern Norton Sound 

that control their extent. These currents are at depth and near the 

surf ace. 

Suspended-sediment concentration decreases and 

The extent of turbid water varies seasonally. It is most extensive June 

through October even though discharge of the Yukon River decreases 

substantially after July. Some turbid water circulates into Norton Sound 

throughout this period. 

immediately offshore from the delta. 

Turbid water is present in May and November but only, 
Figure 1. Landsat TM data recorded on 5 July, 1985. The thermal image is a 

subsection of the data along the boundary of the Alaska Coastal 

and Bering Shelf water-masses. The data have been enhanced using 

an edge-enhancement algorithm. 

shades are cold. Structures in the water are related to the 

mixing of the warm coastal and cold shelf water. 

Light shades are warm and dark 

Figure 2. Landsat TM data recorded on 22 July, 1985. The image is a 

subsection of the data northeast of the Yukon Delta. The data 

have been enhanced using the principal components algorithm 

applied to TM bands 1-4. The first four principal components 

were composited to form the color image. 

vegetation, light blue and white is turbid water from the Yukon 

River and dark blue is clearer water. 

Red is terrestrial 

Figure 3. Landsat TM data recorded on 22 July 1985. The image is the same 

subsection as in figure 2. The image was generated by rationing 

band 1 to band 3 to enhance turbid water features. 

Figure 4. NOAA-AVHRR image recorded on 22 July, 1985. The thermal image 

has been density sliced to display water-masses in the Bering 

Sea. Contoured data are intergrated chlorophyll mg/m2 collected 

by ISHTAR investigators. High concentrations of chlorophyll are 

located in the Bering Shelf water-mass seen as shades of green on 

the image. 

blue is cold oceanic water that upwells near the Siberian coast. 

Bright colors are the warm coastal water and dark 

APPENDIX A 

DISTUBUTI(34 AND CIRCULATION OF TURBID YUKON RIVER WATER 

K. Dean and C. P. McRoy 

Abstract 

The interannual and intra-annual distribution and circulation of turbid 

) 

water was studied in the northeast Bearing Sea. 

from discharge of the Yukon River which is the primary component in the 

development of the Alaska Coastal Current in the area. Landsat MSS satellite 

imagery and ship-based measurements were used to map the distribution of 

turbid water and to analyze flow characteristics. 

transported and deposited northward from the delta across the entrance to 

This turbid water results 

Most of the turbid water is 

Norton Sound June through October. 

deposited into southern Norton Sound. 

similar to the distribution of modern bottom sediments derived from the Yukon 

River. Within the turbid water three zones have been identified based on 

brightness levels. These zones appear to result from the concentration and 

position of suspended sediments in the water column and influence submarine 

biologic activity. 

Approximately 10% is transported and 

The extent of turbid water is very 
. 1 

c 

APPENDIX B 

SATELLITE OBSERVATIONS OF WATER MASSES IN THE NORTHERN BERING SEA 

Kenneson G. Dean 

Geophysical Institute 

C. Peter McRoy 

Institute of Marine Science 

University of Alaska-Fairbanks 

Physical and biological oceanography are being studied in the 

northern Bering Sea using satellite data and ship-board measurements. 

The satellite data, recorded in 1985 and 1986, were acquired by the 

NOM-AVHRR sensor (Advanced Very High Resolution Radiometer), and 

Landsat Mu1 ti-spectral Scanner (MSS) and Thematic Mapper (TM) sensor. 

Sate1 1 i te data was computer-enhanced to optimize the distribution of 

water-masses, suspended sediments, and flow characteristics. Ship-board 

measurements acquired by scientists working on the Inner Shelf Transfer 

and Recycling project (ISHTAR) provided field-data and "ground truth. I' 

Three distinct north-flowing, water-masses occur in the area during 

the ice-free season: Anadyr, Bering Shelf and Alaska Coastal. The 

Anadyr water-mass is located in the western Bering Sea and is derived 

from water that upwells adjacent to the Siberian coast. This water is 

cold (0-5"C), highly saline and nutrient rich. In contrast, the Alaska 

Coastal water-mass is located in the eastern Bering Sea and is strongly 

influenced by river discharge, primarily the Yukon and Kuskokwim Rivers. 

This water is warm (10-20°C) has low salinity and is nutrient poor but 

has high concentrations of suspended sediments especially in the 

vicinity of the Yukon Delta. Between the eastern and western 

water-masses is the Bering Shelf water. This water has intermediate 

temperatures (5-10°C) and nutrient concentrations but has the highest 

levels of phytoplankton productivity or biomass. 

Remote sensing data only records near-surface water temperatures 

and turbidity. 

the satellite data accurately depicts their general distribution, 

boundaries and flow characteristics. This analysis provides baseline 

information of a pristine shelf environment, with abundant marine life, 

that is destined for petroleum and harbor development. 

Due to the distinct characteristics of each water mass,