Arabian Sea

The Arabian Basin

The southern limits of the Sea are dominated by the Arabian Basin, which reaches depths of over 4,500 metres (14,764 ft), and which maintains a relatively constant depth throughout.^[10] The Carlsberg Ridge flanks the southern edge of the basin.

The deepest parts of the Arabian Sea sit in the Alula-Fartak Trough on its western border with the Gulf of Aden. The trough, which reaches depths of over 5,360 metres (17,585 ft), runs through both bodies. The deepest known point in the Arabian Sea sits at a depth of 5,395 metres (17,700 ft).^[where?] Other significant deep points sit within the Arabian Basin, including a 5,358 m (17,579 ft) deep point off the northern limit of Calrsberg Ridge.^[6]

The continental shelf line is relatively narrow along the Makran, Arabian, and East African coastlines; conversely, its extends greatly from the coast of much of the Indian subcontinent, reaching distances exceeding 300 km (190 mi) in some places.^[11] The structure of the shelf line played a significant role in the creation of the Indus Fan, which was flooded and submerged along with the rest of the Indian coast at the end of the Last Glacial Maximum (LGM).

Other features

The Falaj Valley, discovered in 2009 by French surveyors, is an underwater valley off the eastern coast of Ash Sharqiyah Region in Oman. It is 81 kilometers wide, with a maximum depth of 3,097 metres (1.924 mi) and a relief of 1,151 m (3,776 ft), extending out roughly 75 km (47 mi) from the shelfline. It is named for the Falaj Irrigation System, a network of aqueducts, conduits, canals, and drainage systems built expansively across eastern Oman in the 5th century to equitably provision and maintain water supplies for villages and other settlements as groundwater sources depleted in that era.^[16][17]

Owen Fracture Zone

The De Covilhăo Trough, discovered in 1930 and named for 15th century Portuguese explorer Pero de Covilhăo, reaches depths exceeding 4,400 metres (14,436 ft).^[18] It and the Murray Ridge on its western border separate the Indus Fan from the Oman Abyssal Plain,^[19] which leads on into the Gulf of Oman. The Murray Ridge arguably acts as an extension of the Owen fracture zone, an extensive bathymetric ridge running from the northwestern to southwestern Arabian Sea along a line roughly parallel to the southern Arabian and eastern Somalian coastlines, stretching from the central Makran coast to a point roughly 500 kilometres (310 mi) east of the central Somalian coastline.^[10][20][21] The zone is characterized by steep slopes reaching heights of nearly 2,000 metres (6,600 ft) relative to the surrounding seabed. The fracture zone has acted as a natural barrier preventing sedimentation from the Indus Fan from extending out into the Oman Basin.^[22]

Oceanic fronts and boundaries

The Arabian Sea is bounded on its southwest by the Carlsberg Ridge and Horn of Africa, on its west by the Gulf of Aden, on its northwest by eastern Yemen, Oman, and the easternmost point of Iran, on its north by Pakistan and Western India, and on its southeast by the Laccadive Sea and the westernmost islands of Lakshadweep and the Maldives. It consists of 7 ecological oceanic fronts, with the typical and most prominent upwelling fronts along the coasts of India and Pakistan. The 4 fronts which sit in or within the immediate environs of the Arabian Sea are delineated as follows:^[23]

• The Gulf of Aden Front (GAF): Forming a concave semicircle running from Burua in Somalia (11°28′45.519″N 49°41′23.6934″E) to the village of Khird in Yemen, 5-10 miles east of Al-Shihr. It's sagitta is roughly 30–40 kilometres (19–25 mi).
• The Oman Coastal Front (OCF): Shielding the coastline from Cape Fartak (15°37′59.4″N 52°13′31.5″E) to Masirah Island (20°5′56.7″N 58°36′56″E).
• The Gulf of Oman Front (GOF): Bordering the coastlines of Iran and the Arabian Sea to produce a three-sided wall around the Oman Abyssal Plain, running from Ras al Hadd at the plain's northwestern limit (25°17′39″N 57°5′0″E) near the entrance to the Strait of Hormuz. The area of the Iranian Coast moving east contained within this shield is the main northern stretch of coastline for this hydrological environment. That mass is then separated on the east by a convex shield stretching roughly from the Ziyarat Peninsula (25°20′32.7″N 59°53′36.5″E) back to Ras al Hadd, with a sagitta of roughly 40–50 km (25–31 mi).
• The West Indian Shelf-Slope Fronts (WISSF), stretching along the western Indian coastline, additionally containing two separate and hydrologically distinct regions with different outflow, tidal, and sedimentary properties from the wider frontier:
  • The Indian Estuarine Front (IEF): Forming a relatively flat shield stretching from Ras Malan (25°18′55.4″N 65°13′12.6″E) in Pakistan to the northwestern tip of the Kathiawar Peninsula in India; it encompasses the immediate drainage channels of the Indus River and surrounding source rivers.
  • The West Indian Mid-Shelf Front (WIMSF): Encompassing the watershed of the Gulf of Khambat.

Fronts are largely seasonal, and can be pronounced, exceeding 5° C (9° F) in some places.^[24] The Arabian Sea LME ultimately ends on a line stretching northwest from 200 km (120 mi) south of Cape Comorin in India to midway between Ras Hafun and Cape Guardafui on the eastern Somalian coast, it extends several hundred kilometers north of the Carlsberg Ridge across most of its expanse, only coming within a few hundred kilometers of the uplift zone upon reaching the East African shelf line.^[23]

Border and basin countries

Coastline of border and basin countries:

1.  India - 2,500 kilometres (1,600 mi)
2.  Pakistan - 1,050 kilometres (650 mi)^[25]
3.  Iran (Makran Coast) - ~ 130 kilometres (81 mi)^[26][27] (No coastline on the Arabian Sea according to IHO delineations)
4.  Maldives - None (contained by Laccadive Sea)
5.  Oman (Excluding Gulf of Oman) - ~ 720 kilometres (450 mi)^[28]
6.  Yemen (Including Gulf of Aden) - ~ 1,640 kilometres (1,020 mi)^[29][30]
7.  Somalia (Cape Guardafui to Ras Hafun) - ~ 200 kilometres (120 mi)^[31]

Seamounts

Prominent sea mounts off the Indian west coast include the Raman and Panikkar Seamounts, named for Nobel Laureate in Physics Sir Chandrasekara Venkata Raman, and N. K. Panikkar, founder of the Indian National Oceanographic Institute, respectively.^[32][33]

Sind'Bad Seamount, named for the mythical sailor of Arab and Persian literary tradition, and Zheng He Seamount, named for the Chinese admiral and explorer who charted the Indian Ocean and Arabian Sea for the Ming Dynasty in the 15th century, are some notable seamounts in the western Arabian Sea.^[34][35]

The Sadko Seamount is the only seamount in the central Arabian Basin, and the only one known to be present in the west as far south as the Carlsberg Ridge.^[36][37] It is named for Sadko, a hero of Russian folklore, who sinks to the bottom of the Indian Ocean after angering Tsar Morskoi, the King of the Sea.^[38]

Temperatures and Arabian Sea warming

Historically, minimum air temperatures of about 24 to 25 °C (75 to 77 °F) occurred between January and February, typically only exceeding 28 °C (82 °F) (via extension of the Indo-Pacific Warm Pool) between June and November.^[5] Most extreme surface temperatures typically occurred in the Persian Gulf;^[46] however, vacillating temperature extremes and dramatic meteorological events have become far more commonplace in recent years, producing significant fluctuations in this pattern.^[46][47][48]

Studies reviewing data up to the turn of the 3rd millennium indicate that sea surface temperature (SST) normals have increased by roughly 0.84° C (~1.3–1.5° F) on average over the past 100 years.^[46] The sea's all time minimum temperature occurred in 1975, its all time maximum in 1998. Rapid warming from 1985–87 was responsible for the prolonged pattern of increasingly warm air seen in the region today.^[23] Recent studies by the Indian Institute of Tropical Meteorology confirmed that the Arabian Sea is warming monotonously.^[49][50][51] Experts have consistently pointed to climate change and global and regional heating as playing a principal role in this trend.^[52][53] The intensification and northward shift of the summer monsoon low-level jet over the Arabian Sea from 1979 to 2015 has led to increased upper ocean heat content, due to enhanced downwelling and reduced southward heat transport.^[50] In much of the southeast Arabian Sea, the annual period during which Sea surface temperature normals exceeded 28 °C (82 °F) increased in length by roughly a month on average between 1982 and 2020.^[54] Indian oceanographers began recording SSTs exceeding 32 °C (90 °F) in localized areas of the same region as early as 2007.^[48] Moreover, 2024 stood as the hottest year in the Middle East on record, contributing to warming waters.^[47]

The monsoon seasons

In mid to late summer, strong southwesterly winds blowing from the Horn of Africa and western Indian Ocean carry warm, moist air northeastwards, contributing to strong oceanic forcing across the Arabian Basin. This forcing produces the prototypical rainy period of the South Asian monsoon season, alongside numerous additional annual environmental and meteorological shifts throughout the region.^[55] The winds produced during the southwest monsoon over the Arabian Sea, often referred to as the Findlater Jet, are heavily uniform northeastwards, and the strongest witnessed anywhere outside the Southern Ocean.^[56] The southwest monsoon is preceded by the Arabian Sea Mini Warm Pool (ASMWP), a period of 2 to 3 months prior to the beginning of the summer monsoon wherein SST averages exceeding 30 °C (86 °F) persist across much of southeastern basin.^[48] This gradual heating is reversed by mid-winter, when shallow, northeasterly winds carrying cool, dry air from the Hindu-Kush and Himalayas prevail.^[56][57]

The summer monsoon has begun to lengthen and accelerate in recent decades, with extreme rainy seasons repeatedly striking the Persian Gulf and South Asia since the start of the 2020s.^[52][53] It has become more erratic as well, resulting in heavy, violent, short-lived systems striking randomly and unpredictably within the basin.^[52] These systems and other extreme climactic fluctuations have killed thousands across large parts of Asia.

The Arabian Sea LME

The Arabian Sea large marine ecosystem (LME) is an ecological region encompassing an area of approximately 3,900,000 km² (1,500,000 sq mi) within the sea, Gulf of Aden, and Gulf of Oman below the continental shelf line, representing all populations of non-coastal marine life within the Arabian Basin..^[58][60] Though the Persian Gulf is included in this region as well, it may be excluded from certain analyses and accounts of the ecosystem, owing to the significant difference between its physical and hydrographic characteristics and those of the larger basin.^[58] In either case, the Arabian Sea LME remains one of the most ecologically productive regions on the planet, owing to the vast store of nutrients driven up to the sea's surface each year by intense oceanic upwelling in the fall and summer months.^[60]

The Arabian Sea LME is known to contain nearly 330 species of coral, 550 species of mollusk, 200 species of crab, 20 species of marine mammal, and more than 1,200 species of fish. On account of extreme SSTs in the Persian Gulf exceeding 34 °C (93 °F), extensive coral bleaching has been observed in parts of the ecosystem.^[46]

Despite its productivity, coastal pelagic fish populations in the region are relatively sparse, believed to be a result of unfavorable feeding conditions that discourage spawning of larvae. These conditions, in turn, are caused by incorrect mixing of the surface layer which results from the highly intense summer monsoon and the strong, current producing winds it creates in the sea's north and west.^[59]

Mangrove forests

Most substantial mangrove ecosystems in the Middle East are clustered along the coasts of the Persian Gulf and Red Sea, with smaller pockets situated on the Gulf of Oman and Makran coastlines. Coastal forests along the Arabian Sea are relatively small in expanse compared to those of other parts of the world, being restricted almost entirely to regions north of the Arabian Peninsula, the principal exception being a substantial cluster surrounding Masirah Island off the coast of southern Oman.^[44]

Threats

The Arabian Sea's coastal and marine ecosystems face significant threats from human activity, including shipping, oil and gas extraction, military conflict, coastal development, and water desalination.^[63]

The monsoon variable

In the era of square rigged vessels, the Arabian sea trade was effectively governed by the Northeast-Southwest Drift pattern of the northern Indian Monsoon Current. Northeasterly winds dominated in the summer months, allowing traders embarking from East Africa, the Horn of Africa, and the Arabian Peninsula to sail north and eastwards towards South Asia and the Bay of Bengal. Once there, early Arabian Sea traders were essentially trapped, marooned at their destination until the reversal and softening of the winds and ocean currents, which would enable them to sail home on calmer waters.^{[57][70][73][74]} This dynamic, combined with the desolate geography and inaccessibility of long stretches of the Arabian shoreline, made contact with one's point of origin before the beginning of the favorable monsoon regime effectively impossible.^[69] Routes during this period were thus heavily segmented, with sailors at each leg of the journey holding an effective monopoly on goods from markets in the east in the west, and vice versa.^[70][75][76]

The development and diffusion of the first fore-and-aft rigged vessels by Arabian Sea merchants in the early 1st millennium CE revolutionized shipping in the Arabian Sea and across the wider Indian Ocean. The lateen sail allowed sailors to angle their movement against the prevailing wind current, greatly improving maneuverability and widening ships' potential bearing options.^[75][77] This development extended and expanded the range of merchants travelling along the Indian Monsoon Current, opening routes to the East Africa, the Horn of Africa and Arabia via Southern India and the islands of the Laccadive Sea, and expanding the scope of trade along the northern Arabian Sea coastline.^[70][78] The advancement was less revolutionary here than in other regions, though, on account of the hesitancy of merchants in the Western Indian Ocean to ride against the wind using sailing techniques enabled by the mechanism.^[75]

The common assumption that Arab traders invented the lateen sail and diffused it to neighboring regions^[77] has been challenged by some scholars since the end of the 20th century.^[75][79] Merchants in Arabia were relatively late to develop an extensive seafaring culture, supporting the notion that the version of the sail used in the Indian Ocean was invented by a broader 'West Asian' seafaring culture in contrast to any one particular group or polity. The Periplus of the Erythraean Sea does support the notion that Oman served as an important producer of the lug vessels which preceded lateen-based versions of the dhow. Regardless, the development and prominence of the lateen dhow, as well as the historical use of the term 'Arab' in the West to describe groups to the east of the Mediterranean ranging from Egyptians, to Persians, to Indians may have informed later historiographical and linguistic readings of primary documents as attributing creation of the technology to populations contemporarily defined as being Arab. The lateen is ultimately theorized to have been developed independently by sailors in the Indian Ocean (7th century), Mediterranean (5th century),^[80] and East/Southeast Asia at different times over the course of the first millennium.^[75]

Beginnings through Antiquity (4000 BC – 600 CE)

Trade along the Makran and Arabian shoreline is evidenced to have occurred as early as the 4th millenium,^[81] whilst sea-borne trade possibly began as early as the 3rd millennium, certainly by the late 2nd millennium in the early stages of the Age of Sail.^[82] Early traders moved along the coast in reed boats and canoes, trading at local settlements and trading hubs along the way.^[72] Modern evidence points to a sea-borne trade between the kingdoms of Mesopotamia and the Persian Gulf, Ancient Egypt, and the Indus Valley Civilization along the Arabian coast dating to the late 3rd millenium.^[83] Translated cuneiform texts from the reign of Sargon of Akkad point to an extensive ship building industry centered at Akkad, and an equally extensive sea-borne trade between his empire, Tilmun, a collection of coastal trading hubs in present day Qatar, Bahrain, and Eastern Saudi Arabia, Magan, a civilization on the Gulf of Oman, and the Indus Valley Civilization (Meluhha).^[84]

Major Harappan ports included Kanjetar, Megham, and Lothal, one of the earliest if not the earliest known port of the Bronze Age to have an artificial dock with water-locking arrangements, situated along a route running from the Makran Coast to the Indus River Delta, on to sites once located on rivers draining into the Gulf of Khambat.^[81][82] Little archaeological evidence exists of any Harappan vessels which would have been used in the trade, apart from illustrations found on ceramics and cuneiform tablets from that period, and remnants of a ship in Oman carrying beads originating in India.^[4][82][85] Contact between Egypt and Punt began with the Eighteenth Dynasty under Hatshepsut in the early 15th century BC; merchants of this trade, though, mainly traversed the Red Sea and or tributaries of the Nile.^[81]

By the time of Julius Caesar, several well-established combined land-sea trade routes flowing to the Roman Empire depended upon water transport through the Arabian Sea around rough and desolate inland terrain features to the sea's north.^[70][86][87] Trade between Egypt and India greatly increased during this period, predominantly via square-sailed Mediterranean vessels.^[69][75] These routes usually began in the Far East or down river from Madhya Pradesh, India with transshipment via historic Bharuch (Bharakuccha), traversing past the inhospitable coast of modern-day Iran, then splitting near Hadhramaut in south-central Arabia into two streams heading northwards, either by land along the Red Sea, or by sea via the Gulf of Aden through the Bab-el-Mandeb, and thence into the Levant, or south on to Alexandria via Red Sea ports such as Axum.^{[76][88][better source needed]} Outgoing Roman vessels would split at the Bab-el-Mandeb, some heading eastwards towards India with the monsoon wind, about a year's journey, the remainder heading south towards Rhapta, near present-day Dar es Salaam, a roughly two year voyage going one direction.^[89] At this time, depending on one's location and place of origin, the standard lingua franca of commerce may have been Greek, Prakrit, Sanskrit, or Aramaic, among others.^[69]

Good transport along the southern coastal route past the rough country of the southern Arabian Peninsula by sea was significant, and thus the Egyptian Pharaohs built several shallow canals to service the trade, one more or less along the route of today's Suez Canal, and another from the Red Sea to the Nile River; both shallow works were ultimately swallowed up by huge sand storms in antiquity. Each major route in both regions involved the transshipment of goods on to pack-animal caravans, which then travelled through desert country, a journey often interlaced with extortionate tolls levied by local rulers.^{[citation needed]} Arab merchants were already engaged in trade with East Africa by this period, with additional maritime routes developing in the Persian Gulf by the 3rd century CE. Trade on all routes is thought to have been heavily localized, with goods travelling from one merchant to the next along the coast, creating a virtually monopolized marketplace at each location.^[88] Trade with Sri Lankan markets in the western Indian Ocean, for instance, was conducted by Persian merchants, who continued the route on past the Levant and Arabian Peninsula.^[74][75] South Indian and Sri Lankan traders, in turn, continued the route on towards Oceania and Southeast Asia, and so on.^{[citation needed]}

The Arabian Sea is described at length in the Periplus of the Erythraean Sea ("The Circumnavigation of the Red Sea"), a mid-1st century Greek merchant text detailing the trading corridors linking the Indian, East African, Arabian, and Mediterranean worlds.^[87][90] The work is believed to be largely accurate as relates to the polities and trading conditions of the Red Sea, Gulf of Aden, and the Arabian Sea shorelines of India, Arabia, and the Makran.^[88] Recent investigations, though, have led to skepticism concerning the presence and significance of Mediterranean traders in the Arabian Sea during this period, on account of the work's inaccurate depictions of regions largely unknown to them except through merchants operating in the immediate maritime environs of the Egypto-Mediterranean world.^[69][88]

Middle Ages to Portuguese Contact (600 – 1498 CE)

Trade exploded in the Arabian Sea with the emergence of Islam and the subsequent unification of the Arab, Persian, and Egyptian worlds under a singular religious, cultural, political, and thus, effectively, maritime banner. Scholars at madrasas and universities across the lands of the first three caliphates produced substantial advancements in physics, mathematics, shipbuilding, and astronomy which greatly assisted and enhanced the execution of long-distance trade.^[77] Developments such as these were spurned by knowledge of sailing and oceanography handed down to them by the Persians, with the most advanced long-distance vessels used by Arab merchants typically being produced in India during the Rashidun era.^[75] These advancements were eventually widely diffused across the continent as far as Europe and China, spurring the growth and development of an extensive Old World maritime trade network operating in tandem with the Silk Road.^[21][77] This, combined with the substantial prevalence of Muslim merchants along southern maritime trade networks as a result of it led to Arabic becoming the de-facto language of commerce across the Indian Ocean.^[57] Arab dominance of the trade would last until the arrival of European powers in the 15th and 16th centuries.^[71]

The superior freight capacity and efficiency of sea-transport led the Maritime Silk Road to gradually overtake the overland Silk Road in terms of importance and volume of goods trafficked.^[87] Though the overland route did not experience its peak until the Mongol Era, the collapse of this system of rule and the subsequent chaos it engendered across much of the interior drove many merchants seawards, exacerbating the shift away from the overland trade.^[57] Ship transport would overwhelmingly eclipse the Silk Road during this period, marking the start of the final stage of the routes' history, ending with its effective demise in the 16th century.^[71]

Imperialism, conflict, and migrant communities – societal consequences of the trade

The prevalence of interregional maritime trade in the Arabian Sea and wider Indian Ocean encouraged the creation of numerous diasporic communities across its disparate regions over millennia. Diasporic communities, even if they held on to their traditional beliefs and cultural practices, became part of a heavily mixed, highly heterogeneous society. Rarely were the terms of trade or of one's identity defined on the basis of nationality; rather, one's community and region of origin played a far more substantial role in the substance and particularities of their dealings abroad. Ties were built on the basis of shared religious, linguistic, or (as in cases of trade within the borders of or on behalf of the region's various empires) political heritage. ^[69][88]

Evidence from the Periplus of the Erythraean Sea points to the development of intercultural diasporic merchant communities in Rhapta (East Africa), Punt/Axum (modern-day Eritrea), Socotra, and Muziris by no later than the turn of the 1st millennia. Indian trading diasporas are thought to have developed in Egypt and Oman, and pilgrimages carried out at sites of worship on Socotra during the same period. Archaeological evidence shows that merchants from the Roman city of Palmyra in central Syria played a central and critical role in the facilitation of trade between the Indian Ocean world and the Roman Empire in the Red and Arabian Seas, not unlike the Italian merchant communities which would come to exist in the Mediterranean centuries later.^{[69][71][87][88]} Palmyrene merchant networks were highly centralized, and their interactions heavily identity dependent, with intensive ties stretching back to aristocratic families in the , which could be used to reward or punish merchants for acting in or out of accordance with group norms. Numerous languages were used in trade, dependent upon the region and groups engaged in particular dealings.^[69]

Petroleum and natural gas – shipping & production

A majority of the vast heavy oil and natural gas deposits in the Middle East are located at higher elevations in the Persian Gulf or inland north of the Arabian Basin.^[102][103] Major natural gas deposits, though, have been found on the sea's eastern edge off the coast of Western India.^[104][105] As a result of the former fact, traffic through the Strait of Hormuz on into the Arabian Sea accounts for roughly 25% of the global seaborne oil trade, transporting a majority of the crude oil exports of most Gulf nations.^[106] It accounts for 19% of seaborne LNG trade, representing more than 90% of the total LNG exports of Qatar and the United Arab Emirates.^[103] The vast majority of traffic, in both cases, is bound for Asia.^[103][106]

Commercial fishing & marine resource exploitation

Exploited marine species in the Arabian Sea include Indian oil sardines, typically caught off the west coast of India, and the drum and croaker fish of the family Sciaenidae. Most landing reports only indicate the catch as being a 'marine fish', making a specific cataloguing of exploited species and variants difficult. Large oceanic pelagic fish are popular among commercial fishermen, otherwise. Bombay duck and anchovies are also harvested in significant quantities.^[107] Roughly half the market value of reported landings in the Arabian Sea can be attributed to perch- and herring-like species, with only a small quantity attributed to large marine species such as sharks and rays.^[107]

The Arabian Sea LME was one of the few large marine ecosystems to see little to no growth in commercial fishing yields from the 1990s to 2010s, reaching a settling point of roughly 2 million tonnes in 1990: This represented a quadrupling of fishing yields from 1950 onwards.^[107] Activity in the region has increased recently as a result of the intensive activity from Chinese industrial fishing vessels in the Sea and wider Indian Ocean; these actions have been heavily scrutinized by Western and West and South Asian sources, among them, most notably, the governments of India and the United States.^[108][109]