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.-bY~ rD''''6g~ SEATTLE, WASHINGTON 98105 UNIVERSITY OF WASHINGTON DEPARTMmT OF OCEANOGRAPHY Seattle, Washington 98105 • Articles Concerning Research Sponsored by the Office of Naval Researchs

Technical Report Noo 89

ELECTRONIC DATA PROCESSING IN SEDIMENTARY SIZE ANALYSES, by Joe So Creager, Dean Ao McManus and Eugene Eo Co11ias 0 Journal of Sedimentary Petrology, ~(4)s833-839, December 19620

Technical Report Noo 90

DISTRIBUTION OF LIVING PLANKTONIC FOlWfiNIFERA IN THE NORTHEASTERN PACIFIC, by Ao Barrett Smitho Contributions, Cushman Foundation, 14(1)81-15, January 19630 -

Technical Report Noo 91

A NEW HYPOTHESIS FOR ORIGIN OF GUYOTS AND SEAMOUNT TERRACES, by Yo Rammohanroy Nayuduo Crust of the Pacific Basin, Geophysical Monograph Noo 6, ppo 171-180, December 19620

Technical Report Noo 92 -.'-.- PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A LARGE SPI'lLIKE SHOAL, by Dean 10 McManus and Joe So Creager 0 Journal of Geology, 71(4)8498-512, July 19630 - Technical Report Noo 93

GHA.VITI AND THE PROPERTIES OF SEA WATER, by Ricardo Mo Pytkowicz0 Limnology and Oceanography, 8(2)8286-287, April 19630

Technical Report Noo 94

POSTGLACIAL SEDIMENTS IN UNION BAY, LAKE WASHINGTON, SEATTLE, WASHINGTON, by Dean Ao McManuso Northwest Science, 37(2)&61-73, May 19630

Office of Naval Research Reference M63-46 Contracts Nonr-477(10) November 1963 Project Nr 083 012

RI Chairman

Reproduction in whole or in part is permitted for any purpose of the United States Government PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A LARGE SPI1"LIKE SHOAL

DEAN A. McMANUS AND JOE S. CREAGER

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Reprinted for private circulation from THE JOURNAL OF GEOLOGY Vol. 71, No.4, July 1963 Copyright 1963 by the Unh'ersity of Chicago PRINTED IN U.S.A. PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A LARGE SPITLIKE SHOALl

DEAN A. McMANUS AND JOE S. CREAGER Department of Oceanography, University of Washington, Seattle 5, Washington ABSTRACT Measurements of water temperature, salinity, transparency, current velocities, and sediment distribution are used to interpret the physical and sedimentary environments of a spitlike shoal extending 80 nautical miles north of the western tip of Seward Peninsula, Alaska. The shoal, covering approximately 2,000 square miles, is characterized by slopes of less than 31 feet per mile. Sediment-bearing coastal water passes north­ ward through the Bering Strait and past the shoal at speeds of as much as 50 em/sec. Four sedimentary en­ vironments have been recognized, and their significance with relation to the physical conditions is interpreted. The importance of seasonal variations is mentioned.

INTRODUCTION shoal development characterized by close From August 1 to September 2,1959, and correlation of physical and sedimentary con­ from July 26 to August 28, 1960, the De­ ditions. partment of Oceanography of the Univer­ To better understand the correlation be­ sity of 'Vashington carried outa general sur­ tween these conditions, it is necessary to veyof the southeastern part of the Chukchi first examine each condition independently. Sea (fig. 1). Because the sedimentary environments are Many oceanographic aspects of this largely determined by the physical environ­ broad, shallow embayment of the Arctic ments, the latter will be discussed first. The Ocean are transitional, inasmuch as this is characterization of the physical environ­ the passage area for waters moving from the ments is considered under the topics of Pacific Ocean into the Arctic Ocean. The bathymetry, temperature and salinity, cur­ presence of several shoals, from a few to sev­ rents, and water transparency. eral tens of nautical miles in length along the eastern margin of the Chukchi Sea, suggests PHYSICAL ENVIROXMENT that sediment dispersal here is also in a state BATHYMETRY of transition. The eastern shoreline is domi­ Cape Prince of Wales Shoal is a large nated by a few prominent headlands, be­ lobate feature, consisting of approximately tween which subdued tundra coastal areas .2 X 1010 cubic meters (7 X 1011 cubic feet) lie. The shoals lie on the northern side of the of sediment, that forms a broad rise on the headlands. extremely flat floor of the Chukchi Sea (fig. The largest shoal is Cape Prince of \Vales 2, left). Near Cape Prince of \Vales the depth Shoal, extending northward for 80 miles of water above the shoal is less than 5 from the eastern margin of Bering Strait fathoms, but near the distal end of the shoal, (fig. 1). The large area and volume of this where it attains a maximum width of about shoal, its location adjacent to the constric­ tion formed by Bermg Strait, the active 30 miles, the water depth is almost 25 fath­ movement of the water masses as reflected oms. Both lateral slopes of the shoal have a by the strong currents, and the relation of very low gradient. The steepest gradient on the distribution of sediment to the physical the western slope is only 31 feet per mile, environment, all suggest an active area of and the eastern slope, having essentially the same gradient as the sea bottom northeast 1 Contribution No. 259 of the Department of Oceanography, University of Washington. Manu­ of the shoal, is less than 10 feet per mile. In script received December 24, 1961. general, a practically unmeasurable gradi- 498 PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A SPITLIKE SHOAL 499 ent characterizes the bottom of the south­ gin, the temperature and salinity of the wa­ eastern part of the Chukchi Sea. ter do not directly effect sedimentation. However, these properties are important in TEMPERATURE AND SALINITY identifying the sediment-bearing water Because the deposits of the Chukchi Sea masses. The distribution of temperatures at and Cape Prince of Wales Shoal are of clastic 5-meter depths indicates that a pronounced rather than of chemical or biochemical ori- horizontal thermal gradient exists in the

FIG. I.-Index chart locating large shoals along southeastern margin of Chukchi Sea. Shoal at Cape Prince of Wales is defined by 20-fathom isobath. Other shoals are defined by 5- or 10-fathom isobath. •

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$(J '----~16L-9-.----~.L-.----168""'--.--.:lL""--3...0-.-----'16-1.----' $(J '-----161.-ge----3Q.I.-,----I..LEi8-.-~...... --.J3O-'----I67L..-.--...JxJ

FIG. 2.-Bathymetryand sedimentary environments of Cape Prince of Wales Shoal. Left, bathymetric chart showing spitlike shape of shoal; right, distribution of the four sedimentary environments. Note correlation of environments and bathymetry.

I ," PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A SPITLIKE SHOAL 501 southeastern part of the Chukchi Sea and shown overriding the cooler, more saline wa­ the northeastern part of the Bering Sea. In ter west of the shoal (fig. 3), but isohaline, general, the warmer water is along the coast low-salinity water occurs over the shoal and and the colder water offshore. The 5-meter to the northeast. isotherms tend to follow the isobaths, even The temperature-salinity measurements to the extent of developing a perturbation of indicate the presence of water masses that warm water over and to the sheltered side of can be characterized by temperature and the shoal. At the bottom the isotherms also salinity relationships (Helland-Hansen, show a close correlation with the bathyme­ 1918). The two masses most important in try, and the warmer water is near the coast this shoal development are the warm, rela­ and forms a perturbation on the north side tively dilute, coastal water and the cooler, of the headland of Cape Prince of Wales. It more-saline water offshore. The relationship should be emphasized that these are sum­ between these two water masses is especially mer temperature structures. The tempera­ well shown by temperature-salinity profiles ture structure should fluctuate seasonally, across the eastern part of Bering Strait (fig. because the area is ice-covered for 7 or 8 4). months of the year. Vertical temperature gradients typically CURRENTS reveal a thermocline separating warmer and The distribution of mass in the water col­ nearly uniform surface temperatures from umn, as indicated by the temperature-salin­ the cooler, uniform temperatures at depth ity relationships, is related to a fairly strong (Fleming et at., 1959, p. 8). However, differ­ current setting northward through Bering ent vertical distributions were observed at Strait (LaFond et al., 1949, p. 48). Early stations near and over Cape Prince of Wales current determinations, made from dynamic Shoal (fig. 3). Station 35, located near the computations, indicated a general north­ Cape, represents the Alaskan Coastal Wa­ ward surface flow of water in the Bering and ter, identified by Saur et at. (1954, p. 9), al­ Chuckchi Seas paralleling the coast and bot­ though with slightly different absolute val­ tom contours (Barnes and Thompson, 1938, ues of temperature and salinity. Stations 34 p. 66), but computed velocities were found and 49 are west of the shoal and indicate the to be less than observed velocities because overrunning of the deeper water by the the bottom waters were in motion toward warmer coastal water. Stations 40, 43, and the north. 45 display isothermal relationships above The currents measured at 5-meter depth and to the sheltered side of the shoal. Uni­ with Ekman and Gemware current meters formi ty of temperatures from the surface to during August, 1959, and with a modified the bottom, far to the east, was also ob­ Magnesyn current meter during August, served (Ozturgut, 1960, p. 23) near the 1960, showed a northward set (fig. 5, left). As coast between Shishmaref and Cape Espen­ shown by figure 5, the highest speeds (those berg. greater than 50 cm/sec) were recorded set­ The salinity structure in the Chukchi Sea ting northwest, parallel to the coast, just roughly parallels that of the temperature. south of the headland of Cape Prince of The less saline waters are near the coast, and Wales and passing northward through the irregularities in the salinity distribution of strait. The high speed at this location is these waters are effected by the headland of thought to be due to convergence caused by Cape Prince of Wales. The vertical distribu­ the westward-projecting coastline (Fleming tion of the salinity in the Chukchi Sea shows et al., 1960, p. 4). Over the shoal and north­ a similarity to that of the temperature, and east of the shoal, the currents have much typically, the halocline is at about the same lower speeds and show a greater variation in depth as the thermocline. In relation to the direction. shoal, the warm, less saline coastal water is Currents measured to within 5 meters of 502 DEAN A. McMANUS AND JOE S. CREAGER the bottom proximate the direction of the bottom currents (30 em/sec and higher surface currents, especially west of the spit speeds) occur in the same locations as do the (fig. S, right). Although near-bottom meas­ strongestsurface currents. Decreased speeds urements south of the Cape are unavailable, and a variety of current directions also char­ the currents at 20-meter depth are com­ acterize movement of the near-bottom wa­ parable with 20-meter depth currents in the ter over the shoal. strait, and indicate th~t the strongest near- Currents recorded in Bering Strait in Au- STA.40 STA.35 1. 4 6 8 10 12°C 2 4 8 8 10 12°C ~ ~--rloooy-..,.,....,..,-r-:-';r"'!"{-ri.....,.-Ir--1f~Trr. ""1 • ~t ~ ffi ' '<":...... I... I-T' · l;j 10 ---\S :i 15 ....,I- __~d~ 31.0 31.5 32.0 %0 31.0 31.5 32.0 %0

STA.43 2 4 , 6 8 10 12 °c (/) 0: lLJ ~r ]~ .49 !to r i 1LI [ :E 31.0 31.5 32.0 %0 I, .34

STA.45 2 4 6 8 10 12°C (J) 'i I 0: , • 1LI r \S lLJ IE 1f ' \ :E \ : 31.0 31.5 32.0 %0

STA.49 STA. 34 2 468 10 12 °c 2 468 10°C

-...._-.. -.....-. " '\S, t I I ,I , •t 31.2 31.4 31.6 31.8 32.0 32.2 32.4%0

FIG. 3.-Vertical traces of temperature and salinity at selected stations on, and adjacent to, the shoal. A pronounced thermocline and halocllne is indicated west of the shoal, whereas isopycnal water is present over the shoal and to the northeast. PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A SPITLIKE SHOAL 503 gust, 1960, after several days of brisk north­ tion zone between the coastal water and the erly winds, were weaker than those observed cooler, more saline, offshore water (Fleming in August, 1959. Local winds probably et at., 1959, p. 6). The flow widens north of "modify, rather than materially affect, the the strait, and it is here that the large Prince speed and direction of the movements on the of Wales Shoal is found. The coastal water surface layer" (Fleming et al., 1960, p. 4). flowing over the shoal moves at a slower Other current observations made in Bering speed. A large, ill-defined eddy motion ap­ Strait include a 21-hour station occupied pears to be present on the sheltered north­ with an Ekman meter (Barnes and Thomp­ east side of the shoal. son, 1938, p. 66) and the stations reported by Ozturgut (1960, p. 12). These additional WATER TRA.~SPARENCY observations also suggest that, although the A discussion of high-speed currents, par­ current through Bering Strait remains ticularly in the coastal water moving paral-

L--.I • MILE FIG.4.-Temperature and salinity profiles across eastern Bering Strait. The coastal water is shown extending far westward as a plume from Cape Prince of Wales. The boundary between the coastal and offshore waters varies somewhat in sharpness and in distance from land. strong, there are some variations in speed leI to the coastline, leads to a consideration and direction. The greatest current varia­ of water transparency and thus of sediment tion is seasonal, for the water is ice-covered transport. Although no direct measurements in winter, but measurements taken in Feb­ of sediment transport have been reported, a ruary (Maksimov, 1945, p. 8) also showed a combination of studies, including bottom current setting northward through the photography, hydrophotometry, and Secchi strait, although the current speed was only disk measurements, aid in giving a tentative one-fourth of that measured in August. picture of the distribution. Thus, the currents are generally unidirec­ Bottom photography in the Chukchi Sea tional, north from the Bering Sea past the and northeastern Bering Sea has produced spit and into the Chukchi Sea. Along the few good photographs because of the tur­ coast southeast of Cape Prince of Wales, a bidity near the bottom throughout most of convergence of the warm, dilute coastal wa­ the area. The locations where relatively ter occurs, producing high-speed currents good photographs have been obtained, such throughout the water column which then as Bering Strait, were in areas of coarse bot­ move into the strait. The strongest currents tom material (LaFond et al., 1949, p. 25). in Bering Strait tend to occur in the transi- In general, the transparency of the water FIG. 5.-Surface and near-bottom current velocities. Left, currents at 5-meter depth; right, currcnts within 5 mcters of the bottom PHYSICAL AND SEDIMENTARY ENVIRONMENTS ON A SPITLIKE SHOAL 505 decreased toward the shore. This opacity is cupying the western flank, (3) a shoal-crest due in part to particulate organic material, environment, and (4) a sheltered-slope en­ predominantly phytoplankton, and in part, vironment on the eastern slope (fig. 2, right). especially near the bottom, presumably to suspended sediment. In some measurements PRESHOAL ENVIRONMENT organic matter was considered to be the The preshoal environment is recognized probable cause of an opacity maximum oc­ in the area immediately west of the shoal, curring immediately above the thermocline and therefore includes the eastern part of (Buffington et al., 1950, p. 24). Bering Strait and the area just north of the At times, the surface coastal water south­ strait (fig. 2, left). In Bering Strait, the mean east of Cape Prince of Wales is of varying grain size is in the granule and small pebble shades of brown. Water samples taken from classes (fig. 6, left), but fine sands are found stations there contain a high concentration in the northern part of the preshoal environ­ of silt particles in suspension. The boundary ment and grade into the silts of the Chukchi between this turbid water and the highly Sea. transparent offshore water may be ex­ Most sediments in the adjacent areas are tremely sharp, as was reported (LaFond et finer than the preshoal gravels, and the 1 tP al., 1949, p. 81) on the eastern edge of to 2 tP class is the coarsest sediment occur­ Bering Strait where the boundary coincides ring in all the environments. The distribu­ with the transitional area of maximum hori­ tion of the 2 tP (medium sand) size grade zontal temperature gradient. (fig. 7, a) best delineates the preshoal en­ Studies of water temperature and salin­ vironment from the others, and shows the ity, currents, water transparency, and esti­ scarcity of coarse material outside this en­ mates of the sediment content permit the vironment. Isopleths of finer material exhib­ identification of two water masses in the it a reversal of this distribution. Silt vicinity of Bering Strait, both of which pass comprises less than 5 percent of the preshoal northward through the strait. A warm, di­ sample and clay-size particles are even less lute, sediment-laden coastal water is found abundant, except along the eastern and southeast of Cape Prince of Wales and pass­ northern margins of the area. ing around the Cape in the shoreward 2 to 3 The sorting of the sediment is relatively miles. This water tends to override the cool, uniform and very poor throughout the en­ more saline, and more transparent offshore vironment (fig. 6, right). In the strait and water, especially when it passes through immediately northward, the very poor sort­ Bering Strait. Upon emerging from the con­ ing is reflected by the gravel mode and a striction of the strait, the water masses di­ "tail" of sand. These samples show very verge, and this is the location of Cape Prince positive skewness. As the mean size de­ of Wales Shoal. creases to the north, a secondary mode ap­ pears in the sand size, reflecting the con­ SEDWENTARY ENVIRONMENTS tinued very poor sorting. Near the northern Up to now the shoal has been considered edge of the environment, however, this sand only as a bathYmetric feature underlying the mode becomes dominant and, because only a various physical environments, but funda­ few granules are present, the sorting is im­ mentally the shoal is a feature of sediment proved. The poorest sorting is along the deposition. The distribution and variation eastern margin. These samples are bimodal, of this deposition is reflected in the four sedi­ a mixture of preshoal gravel and the shoal mentary environments recognized at Cape sands. Because the adjacent current-slope Prince of Wales Shoal: (1) a preshoal en­ environment is the one that more immedi­ vironment, which is found in front of the ately reflects those processes which control shoal, (2) a current-slope environment, oc- deposition, discussion of the eastern part of •

6

• • 4, _----.... • ...... -...... , 4!l' \ 411' 411' .\ • • \ \ • \ • \ \, I •I I• I I I , f I \ --.... I Ill' Ill' I" -""".\ ""I • • ,_.... "" • / • I I I I 6 I I I I ,I ~ 4" tl (; .J 411' £I .· •I • 2.5 • SORTING (PERCENTILE ESTIMATE OF STANDARD DEVIATION IN PHI UNITS) So,L-__...... L.. .l..- ---l_--=~_....L. L___..J SO' I.-__-L. .J.... ---Ji..---.::~...... J.. J___...J)(J

FIG. 6.-Grain size data. Left, chart of mean grain size showing narrow belt of coarse silt extending northward from the Cape; right, chart of sorting values showing the improved sorting on sheltered slope.

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FIG. 7.-Isopleth charts of selected grain sizes: at percentage of medium sand (24)) showing abundance of material in preshoal environment; b, percentage of coarse silt (5 4» with maxima shown in current slope environment and on floor of Chukchi Sea north of the shoal; c, percentage of fine sand (3 q,) showing maxi­ mum on shoal crest; d, percentage of very fine sand (4 ep) with abundance of olaterial distributed on sheltered slope. 507 508 DEAN A. McMANUS AND JOE S. CREAGER the preshoal environment will be included absence of sediment-laden coastal water, under the section on the current-slope en­ and the presence of rich benthic fauna all vironment. indicate that little silt or clay is being trans­ For mineralogic discussion the gravels ported into the area. Although some sand and the finer particles in the preshoal envi­ has probably been introduced into the envi­ ronment will be considered separately. The ronment, most of the sand and the gravel is preshoal gravels consist of subangular thought to be a lag residuum caused by the pebbles of several varieties of sedimentary, winnowing action of the strong currents. metamorphic, and igneous rock types ex­ However, this lag is not considered to be a posed on the mainland and on the Diomede completely stationary deposit, for the Islands. This similarity of composition with tongue of the hornblende-garnet assemblage the subaerial outcrops does not imply that extending northward from the preshoal area the pebbles have been transported into the suggests some northward movement of the preshoal environment but rather that they sand. This movement, coupled with the lag are eroded remnants of bedrock that are origin, is also suggested by the slightly very nearly in situ. greater depths in the strait. This increased Subangular to angular grains of garnet depth is possibly explained by the strong and hornblende are the minerals most char­ northward-setting current that could scour acteristic of this environment. The abun­ the bottom (LaFond et al., 1949, p. 17). Itis dance of garnet is relatively uniform possible that material transported through throughout the area, though a hornblende the strait west of the Diomede Islands is maximum occupies a belt along the western being deposited north of these islands. This margin. This hornblende-garnetassemblage condition is suggested by the influx of unal­ extends northward from the preshoal area tered biotite in that part of the preshoal into the central part of the southeastern area. Chukchi Sea; however, theassemblage is not as abundant in the shoal environments to CURRENT-SLOPE ENVIRONMENT the east. Another significant mineral, bio­ The current-slope environment occurs tite, is very common in the northern part of along the western slope of the shoal where the area. gradients are about 31 feet per mile. The im­ An abundant benthic fauna is present in portant aspect of this environment, there­ the preshoal area as shown by numerous fore, is not the gradient but the characteris­ shells and shell fragments in most of the tics of the current and the associated sedi­ samples. Pelecypods are the most common ment transport. form, although barnacles, echinoids, crabs, The current-slope sediment is finer than and calcareous Foraminifera form a signifi­ any adjacent material, and mean grain sizes cant part of the fauna. Several species of of samples of sediment here show fine sand Foraminifera are present, including many to coarse silt (fig. 6, left). It should be noted large forms, and although the same types that the isopleths along the southeastern are found in the rich fauna of the northeast­ part of the current-slope area are drawn ern Bering Sea, they are not characteristic of with little control farther southeast, and are the fauna in the Chukchi silts north of the thus guided by the bathymetry. Even preshoal environment. though the chart of mean grain size demon­ The preshoal environment thus comprises strates a certain homogeneity in this area a gravel-and-sand area sustaining a rich that is not present in the preshoal area, this benthic fauna. The overriding coastal water homogeneity is better shown by the iso­ does not directly effect the bottom environ­ pleths of 5

REFERENCES CITED BARNES, C. A., and THOMPSON, T. G., 1938, metoder: Forhandlingar redenskapelig Skandina­ Physical and chemical investigations in the viske Naturforsker mote, Juli 1916, p. 357. Bering Sea and portions of the North Pacific LAFOND, E. C., DIETZ, R. S., and PRITCHARD, D. W., Ocean: Univ. Washington Pubs. in Oceanog­ 1949, Oceanographic measurements from the raphy, v. 3, p. 35-79. U.S.S. Nereus on a cruise to the Bering and BUFFINGTON, E. C., CARSOLA, A. J., and DIETZ, Chukchi Seas, 1947: U.S. Navy Electronics R. S., 1950, Oceanographic cruise to the Bering Laboratory Rept. No. 91 (restricted), 96 p. and Chukchi Seas, summer 1949, pt. 1, Sea floor MAKSWOV, I. V., 1945, Determining the relative studies: U.S. Navy Electronics Laboratory Rept. volume of the annual flow of Pacific waters into No. 204, 26 p. the Arctic Ocean through Bering Strait: Problemi FLEMING, R. H., and STAFF, 1959, Oceanographic Arktiki, v. 2 (English translation: Univ. Wash­ survey of the eastern Chukchi Sea, 1 August to 2 ington Library, Microfilm no. 23f, 13 p.). September 1959, Preliminary report of Brown OZTURGUT, E., 1960, Currents and related water Bear cruise no. 236: Seattle, Univ. Washington properties in the Eastern Chukchi Sea: unpub­ Dept. Oceanography, 36 p. lished Master's thesis, Dept. Oceanography, ------1960, Preliminary report of Univ. Washington, 60 p. Broum Bear cruise no. 268, second oceanographic SAUR, J. F. T., TuLLY, J. P., and LAFOND, E. C., survey of the Chukchi Sea, 26 July to 28 August 1954, Oceanographic cruise to the Bering and 1960: Seattle, Univ. Washington Dept. Ocea­ Chukchi Seas, summer 1949, pt. 4, Physical nography, 11 p. oceanographic studies; descriptive report: U.S. HELLAND-HANSEN, B]., 1918, Nogen hydrografiske Navy Electronics Laboratory, v. 1,31 p.