Opinion of the Court

cle 10(1) contains no implicit modifier at all, such as "generally," "normally," or "usually."

Alaska's reading of Article 10(1)'s drafting history is selective. In fact, the drafting history supports a standard at least as stringent as that adopted by the Master. The provision was first introduced at the League of Nations Conference for the Codification of International Law, held at The Hague in 1930. A preparatory committee offered the following as a basis for discussion: "In order that an island may have its own territorial waters, it is necessary that it should be permanently above the level of high tide." 2 Conference for the Codification of International Law, Bases of Discussion, Territorial Waters 54 (1929). A subcommittee revised the definition but retained the element of permanence: “An island is an area of land, surrounded by water, which is permanently above high-water mark." 3 Acts of the Conference 219. When the International Law Commission of the United Nations revived the work of the Conference in 1951, a special rapporteur reintroduced the subcommittee's definition. Report 297.

In 1954, the British delegate proposed adding the modifier "in normal circumstances," so that an island's status would not be questioned because it was temporarily submerged at high tide in an "exceptional cas[e]." See Summary Records of the 260th Meeting, [1954] 1 Y. B. Int'l L. Comm'n 92. The Commission adopted that proposal, id., at 94, and in its final report defined an island as "an area of land, surrounded by water, which in normal circumstances is permanently above high-water mark," Report of the International Law Commission to the General Assembly, Art. 10, U. N. Gen. Ass. Off. Rec., 11th Sess., Supp. No. 9, U. N. Doc. A/3159, p. 16 (1956). In 1957, an internal State Department memorandum evaluating the Commission's work suggested that the words "permanently" and "in normal circumstances" appeared to be inconsistent and could both be omitted, because "current

Opinion of the Court

international law does not purport to solve such minor problems" as how to treat formations that would be submerged at unusually high states of high tide. Alaska Exh. 84A-21 (Memorandum from Benjamin H. Read, Islands, Drying Rocks and Drying Shoals, Sept. 1957, p. 11). The United States presented that position at the 1958 United Nations Conference on the Law of the Sea, arguing that "there is no established state practice regarding the effect of subnormal or abnormal or seasonal tidal action on the status of islands." 3 United Nations Conference on the Law of the Sea, Official Records: First Committee (Territorial Sea and Contiguous Zone), Summary Records of Meetings and Annexes, U. N. Doc. A/CONF.13/C1./L.112, p. 242 (1958). The Conference adopted the United States' recommendation, and excised the words "permanently" and "in normal circumstances" from the definition of an island.

As the Master recognized, in including the phrase "in normal circumstances," the Convention's drafters had sought to accommodate abnormal events that would cause temporary inundation of a feature otherwise qualifying as an island. Report 300. The United States' view that the international definition of an island need not address abnormal or seasonal tidal activity ultimately prevailed. But the change from the Commission's draft to the final language of the Convention did not signal an intent to cover features that are only sometimes or occasionally above high tide. In fact, the problem of abnormal or seasonal tidal activity that the 1954 amendment addressed is fully solved by the United States' practice of construing "high tide" to mean "mean high water." Averaging high waters over a 19-year period accounts for periodic variations attributable to astronomic forces; nonperiodic, meteorological variations can be assumed to balance out over this length of time. See 2 A. Shalowitz, Shore and Sea Boundaries 58-59 (1964). Accordingly, even if a feature would be submerged at the highest monthly tides during a particular season or in unusual weather, the feature might

Opinion of the Court

still be above "mean high water" and therefore qualify as an island.

What Alaska seeks is insular status not for a feature that is submerged at abnormally high states of tide, but for a feature that rises above and falls below mean high watera tidal datum that has already accounted for the tidal abnormalities about which the drafters of Article 10(1) were concerned. Even if Article 10(1)'s drafting history could support insular status for a feature that slumps below mean high water because of an abnormal change in elevation, it does not support insular status for a feature that exhibits a pattern of slumping below mean high water because of seasonal changes in elevation. Alaska nevertheless contends that there is support for according island status to features more "ephemera[1]" than Dinkum Sands. See Alaska Exceptions Brief 45-50. The authorities Alaska cites all predate the Convention and are therefore unhelpful in construing Article 10(1). Alaska also relies on an analogy to the "mudlumps" of the Mississippi delta, features whose status under the Convention has never been determined. See Report of Special Master in United States v. Louisiana, O. T. 1974, No. 9 Orig., p. 4 (filed July 31, 1974) (concluding that Louisiana's Submerged Lands Act grant could be measured from two mudlumps, but not deciding whether the mudlumps were islands under Article 10(1) or low-tide elevations under Article 11(1)); United States v. Louisiana, 420 U. S. 529 (1975) (overruling exceptions).

In sum, the Convention's drafting history suggests that, to qualify as an island, a feature must be above high water except in abnormal circumstances. Alaska identifies no basis for according insular status to a feature that is frequently below mean high water.

B

In disputing the Master's factual conclusion that Dinkum Sands is "frequently below mean high water," Report 39, Alaska relies on three cartographic sources. First, two nau

Opinion of the Court

tical charts produced following a 1949-1950 survey of the Beaufort Sea by a United States Coast and Geodetic Survey party depict Dinkum Sands as an island, consistent with a survey note describing a "new gravel bar baring about three feet" at mean high water. Alaska Exh. 84A-203 (U. S. Coast and Geodetic Survey, Descriptive Report to Accompany Hydrographic Survey H-7761, p. 3); see Alaska Exh. 84A-202 (U. S. Coast and Geodetic Survey, Addendum to Descriptive Report to Accompany Hydrographic Survey H-7760, p. 4). Second, in 1971, an ad hoc interagency group known as the Baseline Committee, charged with delimiting the United States' coastline, produced baseline charts treating Dinkum Sands as an island. Third, a 1979 map developed for a joint federal-state oil and gas lease sale in the Prudhoe Bay area assigned ownership of a 3-mile belt of territorial sea around Dinkum Sands to Alaska.

As Alaska appears to acknowledge, see Alaska Exceptions Brief 53, the 1971 baseline chart and the 1979 leasing map were based on the 1949-1950 survey rather than independent observations. In 1956, the United States Coast and Geodetic Survey resumed charting Dinkum Sands as a lowtide elevation, based on observations of a Navy vessel made the prior year. It is undisputed that one of the members of the Baseline Committee persuaded the Committee to treat Dinkum Sands as an island based solely on his personal observation of Dinkum Sands as a member of the 1949-1950 survey party. See Alaska Exh. 84A-207 (Department of State, Memorandum to Members of the Baseline Committee, Minutes of Oct. 10, 1979, Meeting, p. 2) (noting that the Committee "has used Dinkum Sands as a basepoint for determining the breadth of the territorial sea . . . because early surveys showed Dinkum Sands to be above high water and Admiral Nygren had personally observed it above high water"). The 1979 leasing map relied on the 1971 baseline chart in assigning Dinkum Sands its own 3-mile belt of territorial sea.

Opinion of the Court

The question, then, is whether the 1949-1950 survey party's conclusion that Dinkum Sands is three feet above mean high water, taken together with visual observations of Dinkum Sands above water, undermines the Master's factual finding that Dinkum Sands is "frequently below mean high water." Report 309. It does not.

Alaska emphasizes that Dinkum Sands has been observed “many times . . . above water" and only "occasionally . . . submerged." Alaska Exceptions Brief 44. But visual observations of Dinkum Sands are not dispositive; the question is not whether Dinkum Sands is above or below high tide on any given day, but where the feature lies in relation to mean high water. To address precisely this problem, the parties jointly commissioned a $2.5 million study to calculate mean high water in the feature's vicinity and to determine the feature's elevation in relation to that datum. First, using a year of tidal readings, the National Ocean Survey computed a mean high-water datum at Dinkum Sands and calculated an error band to account for the fact that the level would ordinarily be based on 19 years of readings. Second, an engineering firm measured Dinkum Sands' highest points in March, June, and August 1981.

Comparing the feature's highest elevation measurements to the mean high-water level, the Master found that Dinkum Sands was not above mean high water at any time it was surveyed. The two highest points of the survey were within the error band for the mean high-water level, but the Master found this fact to be of little weight because the measurements were likely taken from piles of gravel disturbed by the March measurements, rather than from Dinkum Sands' true highest points. Alaska continued to measure Dinkum Sands in relation to mean high water in 1982 and 1983. The feature was found to be above mean high water on a visit in July 1982. By September, the feature had fallen in elevation, possibly by more than a foot, see Report 281-282, placing it below the mean high-water datum.