ACCESS NUMBERS: TO-14195 and 15167 

STUDY TITLE: Historical changes in trace metals and hydrocarbons in the inner shelf sediments, 

Beaufort Sea: Prior and subsequent to petroleum-related industrial developments 

REPORT TITLE: Historical Changes In Trace Metals And Hydrocarbons In The Inner Shelf Sediments, 

Beaufort Sea: Prior And Subsequent To Petroleum-Related Industrial Developments 

CONTRACT NUMBERS: 14195 and 15167 

SPONSORING OCS REGION: Alaska 

APPLICABLE PLANNING AREA: Beaufort Sea 

FISCAL YEARS OF PROJECT FUNDING: FY 1997–1998 

COMPLETION DATE OF REPORT: December 2001 

COST: FY 1997: $135,414; FY 1998: $85,857; CUMULATIVE PROJECT COST: $221,271 

PROJECT MANAGER: A. Sathy Naidu 

AFFILIATION: University of Alaska Fairbanks 

ADDRESS: Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, AK 99775-7220 

PRINCIPAL INVESTIGATORS*: A. Sathy Naidu, J.J. Kelley, J.J. Goering 

KEY WORDS: trace metals, hydrocarbons, contaminants, sediments, Beaufort Sea, Alaskan Arctic 

BACKGROUND:

In recent years, considerable attention has been given to assessing the state of the arctic environment, 

especially in relation to the presence and biological effects of anthropogenic contaminants. The arctic 

region, most of which lies far away from major industries, is no longer pristine as attested to by the levels 

of industrial contaminants found in the environment. In order to understand the sources and processes of 

trace metal and hydrocarbon bioaccumulation in the Alaskan arctic seas, it is pertinent to first document 

the regional concentrations and historical changes in trace metals and hydrocarbons in the sediments. 

Such information will be critical for any effort relating to ecological risk assessment of marine areas with 

the potential for high input of anthropogenic inorganic and organic contaminants. Marine sediments, 

which serve as an initial sink for particle-reactive trace metals and hydrocarbons, could be a major source 

of contaminants for benthic animals and other organisms having a close link with sediments and which 

can serve as pathways for the contaminants to higher trophic levels. For the Alaskan arctic seas however, 

very little information is available on bioaccumulation of contaminants and the pathways involving 

sediments therein. 

The possible anthropogenic sources in the Beaufort Sea could be industrial activities such as the Endicott 

and Prudhoe Bay projects, the ongoing projected or potential oil prospects, Outer Continental Shelf 

(OCS) oil and gas development, or offshore dredging for gravel. It is possible that sediments located 

along the north arctic coast contain such high levels of contaminants that they could result in deleterious 

effects on the region’s biota. Considering these potential hazards, a two-year study (1997–1999) was 

initiated to determine the current concentrations and historical changes in selected trace metals and 

hydrocarbons in sediments from the nearshore of the Alaskan Beaufort Sea. This report addresses the 

results of that study. 
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OBJECTIVES:

The specific objectives of the study were to determine historical changes in the concentrations of V, Cr, 

Cu, Ni, Zn, As, Cd, Pb and Ba in the sediment mud fractions (<62 μm size), and concentrations of total 

and methyl Hg (THg and MeHg), saturated hydrocarbons (normal and isoprenoid alkanes, triterpenoids 

and steranes) and polycyclic aromatic hydrocarbons (PAHs) in gross sediments of the nearshore Alaskan 

Beaufort Sea, and to assess if any of the changes are related to recent industrial development within the 

study area. 

DESCRIPTION:

In September 1997, van Veen grab sediment samples were collected in triplicate at 21 stations from 

within the study area. Sediment core samples were also collected at two locations. Acid solutions of the 

mud fractions were analyzed for all of the trace elements (except As and Hg) either by AAS/graphite 

furnace or ICP/MS. The As analysis was by Excaliber automated hydride generation AFS. The analysis of 

THg in gross sediment was by CV-AAS, and that of MeHg was by CVAF detector following cryogenic GC 

separation. The sediment geochronology was attempted by the 210Pb- and 137Cs-based methods. The 

saturated fraction of hydrocarbons was analyzed for alkanes by a Varian 3400 GC equipped with an SPI 

injector. Normal and isoprenoid alkanes were quantified by GC/FID by the internal standard method using 

dodecylbenzene. PAHs were quantified by GC/MS in the selective ion monitoring mode using deuterated 

internal standard mixtures. 

Time-series comparisons (at approximately 10-year intervals—1977, 1986 and 1997) of the mean 

concentrations of the trace elements in muddy sediments of the nearshore Alaskan Beaufort Sea, show 

significantly increased concentrations in V in 1986 and 1997 from the initial concentrations measured in 

1977, and in Ba from 1986 to 1997. However, these findings are not reflected in the stratigraphic 

variations of elements in the two cores. The stratigraphy demonstrates net significant decreases up core 

in MeHg, Zn, Cd and Pb accompanied by no significant change in the concentrations of other metals. The 

specific mechanisms and sources for the increased levels of V and Ba, as suggested by the decadal 

comparison of data, are unknown, but are suspected to be linked to petroleum-related activities. Despite 

these increases, the levels of all the elements (including V and Ba) in 1997 samples are within ranges 

similar to those in unpolluted nearshore marine sediments of the world. 

Multiple and partial correlation coefficient analyses suggest that in the sediments V, Cu, Ni, Zn, As and 

Mn are chelated with organic matter, and some of the V is also absorbed in the clays. Cluster analysis 

demonstrates the presence of two predominant station cluster groups. Stepwise multiple discriminant 

analysis indicates that Station Group I, mostly clustered around Prudhoe Bay, has significantly lower 

concentrations of MeHg compared to Station Group II, located east and west of the bay. No geographic 

gradient was noted in the concentrations of any of the elements analyzed. The differences in the groups 

could be related to a number of factors, such as regional differences in inputs of MeHg from natural 

terrigenous or industrial sources, or the Hg methylation process, or differences in gross sediment 

granulometry, or to all three. 

The n-alkane and PAH contents in the Beaufort Sea sediments are relatively higher and the composition 

different from many other regions along the Alaskan continental shelf. The low molecular n-alkanes, 

present in relatively small amounts, are derived mainly from marine productivity. Plant waxes of the 

coastal peats and also possibly some coal residues, contribute to the high molecular weight n-alkanes, 

which are the major components of the hydrocarbon fraction. The triterpenoid and sterane profiles 

reinforce the biogenic origin of the major proportion of the hydrocarbon in the entire study area. Only in 

isolated cases is the petroleum signature clearly documented by the presence of thermally mature 

hopanes and steranes in small amounts. 
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The PAH assemblage in the surface sediments is different from that found in Prudhoe crude oil but is very 

similar to that observed in coastal peat and river sediments. This is consistent with its major origin from 

peats, coals, river sediments and, to a smaller extent, from atmospheric inputs. The relatively light ratios 

(mean: –26‰) of stable carbon isotopes (13C) and high OC/N (11) of organic matter in the sediments 

indicate that a large portion of it is terrigenous in origin. 

SIGNIFICANT CONCLUSIONS:

1. Comparison of the mean concentrations of V, Cr, Cu, Ni, Zn, As, Cd, Pb and Ba in the mud fraction of 

sediments from this study with those reported on muds for the past 25 years for the Alaskan Beaufort 

Sea nearshore indicates no significant difference in all the metals with the exception of V and Ba. 

There are significant increases in V from 1977 to 1986 and to 1997 and in Ba from at least 1986 to 

1997. The reason for the increases in V and Ba in the surface sediment samples is unknown. 

2. Attempts to define the 210Pb- and 137Cs-based geochronologies for the two cores included in this study 

were thwarted because of the very low activities of the two radionuclides. Nonetheless, based on 

extrapolation to the two cores of the mean sediment accumulation rate from other sites within the 

study area, we have deduced the dates of major historical shifts in the concentrations of selected 

metals. However, the time-series changes in the sediment trace metals as identified on a decadal 

basis do not match timewise with the stratigraphic record. The above disparity could be due to 

comparison of samples with different lithology, to loss of portions of the stratigraphic data, or to faulty 

deduction by extrapolation of the sediment accumulation rates to the cores examined. 

3. The increase in MeHg down core is most likely related to increased methylation of Hg in progressively 

more intense anoxic subsurface layers. This process presumably involves an initial scavenging of Hg++

by acid volatile sulfides (e.g., FeS), followed by oxidation of the sulfides and biologically-mediated 

methylation of Hg. This buildup could be recycled physically to the overlying waters and entrained in 

sea ice during the freeze-up process. When released with the spring ice melt, the MeHg could be 

sequestered by the primary producers and eventually pass to a higher trophic level. 

4. Correlation coefficient analysis of all elemental and physical data suggests that most of the V, Cu, Ni, 

Zn, As and Pb in mud are probably chelated (via ligand formation) with organic matter, and some of 

the V is also adsorbed on clays. 

5. The molecular markers investigated in the sediments are of mixed marine and terrigenous origin. 

Generally, the resolved n-alkanes are less and the total PAHs more than that found by others in the 

same region a decade ago. The low molecular n-alkanes, present in relatively small amounts, are 

derived mainly from marine productivity. Plant waxes of the coastal peats and also possibly coal 

residues contribute to the high molecular weight n-alkanes, which are the major components of the 

hydrocarbons. The fingerprint of triterpanes/steranes rather than some internal ratio parameters in the 

current samples helps clearly distinguish the biogenic inputs from petrogenic sources. Only in isolated 

cases is the petroleum signature clearly documented by the presence of small amounts of thermally 

mature hopanes and steranes. Composition of triterpenoids/steranes should serve as an important 

diagnostic tool in future monitoring studies to follow subtle changes in the hydrocarbon inputs to the 

region, especially from oil-related activities. 

6. The PAH assemblage in the surface sediments is different from that found in Prudhoe Bay crude oil, 

but is very similar to that observed in the coastal peats and North Slope fluvial sediments. This is 

consistent with the major origin of the PAHs from peats, coals, fluvial sediments and possibly to a 

smaller extent from atmospheric inputs. Additionally, the relatively light (mean: –26‰) carbon isotope 

ratios (δ

13C) and high OC/N (mean: 11) of gross sediment organic matter reflect a predominantly 

terrigenous source of the sediment hydrocarbons. 
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STUDY RESULTS: 

In summary, our investigation indicates that the study area has remained a relatively clean environment 

as far as the trace metal and hydrocarbon concentrations are concerned, despite the petroleum-related 

industrial activities there during the past 30 years. 

STUDY PRODUCTS: 

Naidu, A.S. 1998. Historical changes in trace metal and hydrocarbon contaminants on the inner shelf, 

Beaufort Sea: Prior and subsequent to petroleum-related industrial activities. University of Alaska Coastal 

Marine Institute Annual Research Review, February 1998, Fairbanks. 

Naidu, A.S. 1998. Historical changes in trace metal and hydrocarbon contaminants on the inner shelf, 

Beaufort Sea: Prior and subsequent to petroleum-related industrial activities. MMS Information Transfer 

Meeting, May 1998, Anchorage. 

Naidu, A.S., L.W. Cooper, B.P. Finney, R.W. MacDonald, C. Alexander and I.P. Semiletov. 2000. 

Organic carbon isotope ratios (δ

13C) of Arctic Amerasian continental shelf sediments. Int. J. Earth Sci. 

89:522–532. (This paper was also presented as a poster display by Dr. Naidu at the NSF-sponsored 

workshop, “Arctic Coastal Dynamics”, held at the Woods Hole Oceanographic Institution, October 1999.) 

Naidu, A.S., J.J. Goering and J.J. Kelley. 1998. Time-series monitoring of trace elements in nearshore 

sediments of the Alaskan Beaufort Sea. Proc.1998 ASLO/ESA Annual Meeting, St. Louis. p. A-63. 

Naidu, A.S., J.J. Goering and J.J. Kelley. 1998. Historical changes in trace metals and hydrocarbons in 

the inner shelf sediments, Beaufort Sea: Prior and subsequent to petroleum-related industrial 

developments, p. 17–39. In University of Alaska Coastal Marine Institute Annual Report No. 5. OCS Study 

MMS 98-0062, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Naidu, A.S., J.J. Goering and J.J. Kelley. 1999. Three-decadal time-series monitoring of trace elements 

in nearshore sediments, Alaskan Beaufort Sea, p. 11 (abstract). In Proceedings Seventh MMS 

Information Transfer Meeting. Alaska OCS Region, Minerals Management Service, January 1999, 

Anchorage. (http://www.mms.gov/Alaska/ess/itm/itm99/itm.htm) 

Naidu, A.S., J.J. Goering and J.J. Kelley. 1999. Historical changes in trace metals and hydrocarbon 

contaminants on the inner shelf, Beaufort Sea: Prior and subsequent to the petroleum-related industrial 

development. University of Alaska Coastal Marine Institute Annual Research Review, February 1999, 

Fairbanks. 

Naidu, A.S., J.J. Goering and J.J. Kelley. 2000. Historical changes in trace metals and hydrocarbons in 

the inner shelf sediments, Beaufort Sea: Prior and subsequent to petroleum-related industrial 

developments, p. 7–8. In University of Alaska Coastal Marine Institute Annual Report No. 6. OCS Study 

MMS 2000-046, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Naidu, A.S., J.J. Goering and J.J. Kelley. 2000. Historical changes in trace metals and hydrocarbons in 

the inner shelf sediments, Beaufort Sea: Prior and subsequent to petroleum-related industrial 

developments, p. 7–8. In University of Alaska Coastal Marine Institute Annual Report No. 7. OCS Study 

MMS 2000-070, University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Naidu, A.S., J.J. Goering, J.J. Kelley and M.I. Venkatesan. 2001. Historical changes in trace metals and 

hydrocarbons in the inner shelf, Beaufort Sea: Prior and subsequent to petroleum-related industrial 

developments. Final Report. OCS Study MMS 2001-061, University of Alaska Coastal Marine Institute, 

University of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region, 80 p. 

Naidu, A.S., J.J. Kelley and J.J. Goering. 1998. Historical changes in trace metals in the inner shelf 

sediments, Beaufort Sea: Prior and subsequent to petroleum-related industrial development, p. 76. In
University of Alaska Coastal Marine Institute Annual Report No. 4. OCS Study MMS 98-0005, University 

of Alaska Fairbanks and USDOI, MMS, Alaska OCS Region. 

Naidu, A.S., J.J. Kelley and J.J. Goering. 2001. Historical changes in trace metals and hydrocarbon 

contaminants on the inner shelf, Beaufort Sea: Prior and subsequent to petroleum-related industrial 

development. Paper presented at the International Workshop on Trends and Effects of Heavy Metals in 

the Arctic. McLean, Virginia, 18–22 June 2001. Extended abstract with tabulated trace metal data 

submitted for inclusion in the AMAP Phase II Program report. 

Naidu, A.S., J.J. Kelley and J.J. Goering. 2001. Heavy metals in arctic marine sediments. Submitted to 

Encyclopedia of the Arctic. Fitzroy Dearborn Publishers, London. 

A set of 35-mm slides showing sampling tasks in the field was also submitted to the CMI office at the 

University of Alaska Fairbanks. 

*P.I.’s affiliation may be different than that listed for Project Manager(s). 
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Study Area Map 

Detail of Study Area