GEOSECS Stations Research Articles

Oxygen minimum zone of the open Arabian Sea: variability of oxygen and nitrite from daily to decadal timescales

Abstract. The oxygen minimum zone (OMZ) of the Arabian Sea is the thickest of the three oceanic OMZ. It is of global biogeochemical significance because of denitrification in the upper part leading to N2 and N2O production. The residence time of OMZ water is believed to be less than a decade. The upper few hundred meters of this zone are nearly anoxic but non-sulfidic and still support animal (metazoan) pelagic life, possibly as a result of episodic injections of O2 by physical processes. We report on discrete measurements of dissolved O2 and NO2–, temperature and salinity made between 1959 and 2004 well below the tops of the sharp pycnocline and oxycline near 150, 200, 300, 400, and 500 m depth. We assemble nearly all O2 determinations (originally there were 849 values, 695 of which came from the OMZ) by the visual endpoint detection of the iodometric Winkler procedure, which in our data base yields about 0.04 mL L−1 (~ 2 μM) O2 above the endpoint from modern automated titration methods. We acknowledge that much lower (nanomolar) O2 values have been measured recently with the STOX (Switchable Trace amount OXygen) sensor in the eastern tropical South Pacific, and that similar conditions may also prevail in the Arabian Sea OMZ. In spite of the error in O2 measurements at vanishingly low levels, we argue that the temporal trends of the historic data should still hold. We find 632 values acceptable (480 from 150 stations in the OMZ). The data are grouped in zonally paired boxes of 1° lat. and 2° long. centered at 8, 10, 12, 15, 18, 20, and 21° N along 65 and 67° E. The latitudes of 8–12° N, outside the OMZ, are treated in passing. The principal results are as follows: (1) an O2 climatology for the upper OMZ reveals a marked seasonality at 200 to 500 m depth with O2 levels during the northeast monsoon and spring intermonsoon seasons elevated over those during the southwest monsoon season (median difference, 0.08 mL L−1 [~ 3.5 μM]). The medians of the slopes of the seasonal regressions of O2 on year for each of the NE and SW monsoon seasons are −0.0043 and −0.0019 mL L−1 a−1, respectively (−0.19 and −0.08 μM a−1; n = 10 and 12, differing at p = 0.01); (2) four decades of statistically significant decreases of O2 between 15 and 20° N but an opposing trend toward an increase near 21° N are observed. The mechanisms of the balance that more or less annually maintain the O2 levels are still uncertain. At least between 300 and 500 m, the replenishment is inferred to be due to isopycnal re-supply of O2, while at 200 (or 250?) m it is diapycnal, most likely by eddies. Similarly, recent models show large vertical advection of O2 well below the pycnoclines and oxyclines. The NO2– distribution, taken as an indicator of active NO3– reduction, does not show a trend in the redox environment for a quarter of a century at a GEOSECS station near 20° N. In the entire OMZ, the regression slopes on year within seasons for the rather variable NO2– do not present a clear pattern but by other measures tended to an increase of NO2–. Vertical net hauls collect resident animal (metazoan) pelagic life in the NO2– maximum of the OMZ at O2 levels well below the lower limit of the Winkler titration; the extremely low O2 content is inferred from the presence of NO2– believed to be produced through microbial NO3– reduction. Instead of the difficult measurement by the STOX sensor, the relation between the very low O2 inferred from presence of NO2– and mesozooplankton should be studied with 100 to 150 L bottles rather than nets. The spatial (within drift stations) and temporal (daily) variability in hydrography and chemistry is large also below the principal pycnocline. The seasonal change of hydrography is considerable even at 500 m depth. Future O2 or nutrient budgets for the OMZ must not be based on single cruises or sections obtained during one season only. Steady state cannot be assumed any longer for the intermediate layers of the central Arabian Sea.

Water Column Profiles of Dissolved Inorganic Radiocarbon for the Kuroshio Region, Offshore of the Southern Japanese Coast

We present the water column profiles (surface to 2000 m depth) for dissolved inorganic radiocarbon (14CDIC) from 2 stations in the Kuroshio region including the Kuroshio large meander (LM) of 2004–2005. Surprisingly, the Δ14CDIC value varied up to 125‰ in the intermediate layer, especially near 600 m depth. In addition, the Δ14CDIC value was approximately − 150‰ at 200 m depth at the northern station of Kuroshio in August 2005. This value is ∼100‰ less than other Δ14CDIC values for the same depth. In comparison, the Δ14CDIC water column profiles for the southern station of Kuroshio and GEOSECS station 224 decrease down to 600 m depth and were similar below 600 m depth. Our results suggest that strong upwelling associated with the Kuroshio LM has a powerful influence on the Δ14CDIC water column profiles in the study region.

Estimates of upwelling rates in the Arabian Sea and the equatorial Indian Ocean based on bomb radiocarbon

Radiocarbon measurements were made in the water column of the Arabian Sea and the equatorial Indian Ocean during 1994, 1995 and 1997 to assess the temporal variations in bomb 14C distribution and its inventory in the region with respect to GEOSECS measurements made during 1977–1978. Four GEOSECS stations were reoccupied (three in the Arabian Sea and one in the equatorial Indian Ocean) during this study, with all of them showing increased penetration of bomb 14C along with decrease in its surface water activity. The upwelling rates derived by model simulation of bomb 14C depth profile using the calculated exchange rates ranged from 3 to 9 m a −1. The western region of the Arabian Sea experiencing high wind-induced upwelling has higher estimated upwelling rates. However, lower upwelling rates obtained for the stations occupied during this study could be due to reduced 14C gradient compared to that during GEOSECS.

Eastern North Atlantic deep-sea corals: tracing upper intermediate water Δ14C during the Holocene

Paired 230Th/U and 14C dating were performed on deep-sea corals (Lophelia pertusa and Madrepora oculata) from the northeastern North Atlantic at ∼730 m bsl to investigate past changes of the thermohaline circulation. These were estimated using the Δ14C value of the upper intermediate waters, based on the 14C ages of the top and base of each coral, where possible, and the 230Th/U dating. The reliability of these estimates was checked by dating two very young corals of the species L. pertusa. One of these corals, collected alive in 1999 AD, gave a 230Th/U age of 1995±4 AD after correction for non-radiogenic 230Th. Another coral, the top of which dated to 1969±6 AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 1960s. The calculated Δ14C values from these two corals agree with those measured at GEOSECS Station 23 in 1972–1973 [Östlund et al., Earth Planet. Sci. Lett. 23 (1974) 69–86] and 1991–1992 [Nydal and Gisfelos, Radiocarbon 38 (1996) 389–406]. This, together with the 100% aragonite content and the δ234U and 230Th/232Th values of all the dated corals, indicates that none of the corals behaved as open systems with respect to their U-series nuclides and that they closely represent the water mass properties in which they lived. The pre-anthropogenic Δ14C value of the North Atlantic intermediate waters was estimated at −69±4‰. The reservoir age varies from ∼400 years to ∼600 years, and this variation is due to atmospheric 14C/12C changes. A reservoir age of 610±80 years, close to the pre-anthropogenic value, was determined from one coral dated at 10 430±120 cal yr BP, when the global sea level was approximately at −35 m [Bard et al., Nature 382 (1996) 241–244]. This suggests a modern-like pattern of the oceanic circulation prevailed in the Northeast Atlantic Ocean at this time although the deglaciation was not completely achieved.

Radiocarbon in the Water Column of the Southwestern North Pacific Ocean—24 Years After Geosecs

In the framework of the Worldwide Marine Radioactivity Studies (WOMARS) project, water profile samples for radiocarbon measurements were taken during the IAEA'97 cruise at 10 stations in the southwestern North Pacific Ocean. While 14C concentrations were rapidly decreasing from the surface (Δ14C about 100‰) down to about 800 m at all visited stations (Δ14C about −200‰), the concentrations below 1000 m were almost constant. Some stations were in proximity to the GEOSECS stations sampled in 1973; thus, 14C profiles could be compared after a 24-yr interval. Generally, 14C concentrations had decreased in surface waters (by 50–80‰) and increased (by about the same amount) in intermediate waters when compared with GEOSECS data. In deep waters (below 1000 m), the observed 14C concentrations were similar to GEOSECS values. The bomb-produced 14C inventory had increased by more than 20% over the 24 yr from 1973 to 1997 and was estimated to be about (32 ± 5) 1012 atom m-2, with an annual 14C flux of (1.3 ± 0.3) 1012 atom m-2 yr-1. The results suggest that bomb-produced 14C has been advected northwards by the Kuroshio Current and the Kuroshio Extension and stored in the intermediate layer as North Pacific Intermediate Water.

Distribution of natural and man-made radionuclides during the reoccupation of GEOSECS stations 413 and 416 in the Arabian Sea: temporal changes

Measurement of natural and man-made 14 C and 3 H and man-made 90 Sr, 239,240 Pu and 241 Am at two GEOSECS stations, GX 413 and 416 reoccupied two decades later are reported. Deeper penetration of nutrient and oxygen-poor intermediate waters along with man-made radionuclides, especially at GX 413 (near Bab el Mandab), are noticeable. The one-dimensional advection-diffusion model using pre-nuclear 14 C data supports this observation as the vertical advection velocity at GX 413 is 11.8 m/y compared to the 3.6 m/y in the central north Arabian Sea (GX 416).

Temporal variation of 137Cs inventory in the western North Pacific

The temporal variation of water column inventories of 137Cs in the western North Pacific was examined. 137Cs in seawater of the western North Pacific has originated mainly from global fallout from atmospheric nuclear weapons tests, which occurred in the early 1960's. In the western North Pacific, the water column inventories of 137Cs were 5200 Bq·m-2 in 1973 (GEOSECS station GX225) and 3400 Bq·m-2 in 1983 (KH-84-3 station AN-1). In 1997, the 137Cs inventory was 2600 Bq·m-2 at station 1 of the IAEA'97 cruise. The global fallout at Tsukuba since 1945 was estimated to be 5600 Bq·m-2 in 1973, 4600 Bq·m-2 in 1983 and 3500 Bq·m-2 in 1997. The water column inventories of 137Cs were 93–74% of the estimated global fallout for the same latitude. The typical features of the temporal variation for three vertical profiles taken in 1973, 1983 and 1997 are the decrease of 137Cs activity in the mixed layer and the gradual increase of 137Cs activity in deeper layers. The proportion of the 137Cs inventory in waters down to 1000 meters was 100% in 1973, 88% in 1983 and 75% in 1997. These findings suggest that large amount of the 137Cs entering through sea surface would remain in the mixed layer for more than a few decades.

Distribution of Radiocarbon in the Southwestern North Pacific

Radiocarbon measurements in seawater samples taken at six stations in the southwestern North Pacific visited during the International Atomic Energy Agency (IAEA) 1997 Pacific Ocean Expedition were carried out at the accelerator mass spectrometry (AMS) facility of the Japan Atomic Energy Research Institute (JAERI). Three stations were located close to GEOSECS stations, and three were in the vicinity of Bikini and Enewetak Atolls, which may be influenced by former nuclear weapons testing. Compared with the GEOSECS data (1973), our results show an increase of 14C in intermediate waters. Furthermore, it is estimated that bomb-produced 14C inventories in the water column have increased by more than 20% during the last 24 years. However, vertical profiles of Δ14C at the stations near Bikini and Enewetak Atolls show a similar general trend to those found in other stations.

Δ14C, ΣCO2 and salinity of the Western Indian Ocean Deep Waters: Spatial and temporal variations

Indian Ocean Deep waters (IDW) show an increase in salinity and ΣCO2 between 64°S and 16±4°N by 0.106–0.110‰ and 82–104 µM kg−1 respectively with a corresponding decrease in Δ14C by 42‰ as revealed by the GEOSECS data (1977–78). The Δ14C‐ΣCO2‐Salinity relationships show better correlation in the western sector. High biological productivity induced changes and corrosive deepwaters could account for ΣCO2 increase in the northern regions. Reoccupation of GEOSECS stations during 1985–95 do not show distinctly discernible short‐term temporal changes in Δ14C, ΣCO2 and salinity.

The marine barite saturation state of the world's oceans

Abstract This paper addresses the question of the eventual control of barium concentration in seawater by an equilibrium with barite. For this, we have used a new thermodynamic model to compute the barite saturation index of ocean waters, mainly from GEOSECS data. Our results show that equilibrium between barite and seawater is reached in a number of places: cold surface waters of the Southern Ocean, waters at intermediate depths (2000–3500 m) in the Pacific, deep waters (2000–3500 m) of the Gulf of Bengal. The only samples for which a slight barite supersaturation is found are the surface waters at GEOSECS station G89 in the Weddell Gyre. Besides these locations, the rest of the world's oceans is undersaturated, as was established by Church and Wolgemuth [Church, T.M., Wolgemuth, K., 1972. Marine barite saturation, Earth Planet. Sci. Lett. 15 35–44.]. There is a return to undersaturation of the water column at depths of about 3500 m in the Pacific and of about 2500 m in the Southern Ocean. The reverse is found for GEOSECS station 446 in the Gulf of Bengal for which the highest Ba concentrations can be found at depth: surface waters are undersaturated and equilibrium is reached below 2000 m. Finally, we briefly discuss the role of biogenic and inorganic processes on barite formation in the ocean as well as the influence of strontium substitution in marine barites.

A study related to the light-lanthanide tetrad effect in northeastern Atlantic (28°N 26°W) in comparison with other oceans

Based on the data published by Elderfield and Greaves (1982) for a water column at a site, GEOSECS station 115, of northeastern Atlantic (28°N 26°W), the light-lanthanide tetrad effect was evaluated by the method developed by Masuda and his collaborators. The extent of variation of this effect is much larger than those observed in Pacific and Indian Oceans. Meanwhile, it intrigues us that the value for the effect in question at the top of the water column is almost the same as that at its bottom. Similar facts are observed generally at water columns of other oceans studied thus far. Features of dependence of Nd concentration on depth and of dependence of Ce and Eu anomalies evaluated on the basis of the same mathematical method are also discussed. A minimum absolute value of negative aberration extremum defining the tetrad effect at station 115 can be ascribed to the outflow from the Mediterranean Sea.

A preliminary study of oceanic bomb radiocarbon inventory in the North Pacific during the last two decades

Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4σθ, the bomb radiocarbon flux below 25.4σθ was over 1 × 1012 atom m-2yr-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4σθ increased from zero to over 10 × 1012 atom m-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb 14C flux of over 1 × 1012 atom m-2yr-1 below 25.4σθ in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb 14C gradually spread southward with about 30 years.

Acantharians: a missing link in the oceanic biogeochemistry of barium

Inductively coupled plasma mass spectrometry was used to analyze the Ba and Sr concentrations of the celestite (SrSO 4) skeletons and cysts of individual acantharian specimens obtained from four diverse areas of the world’s oceans. Acantharian celestite Ba/Sr mole ratios ( χ Ba/ χ Sr) averaged 2.6×10 -3 with minimum and maximum values of 6.1×10 -4 and 2.5×10 -2. Celestite Ba/Sr mole ratios were compared to dissolved Ba and Sr concentration ratios ([Ba 2+] T/[Sr 2+] T) derived from GEOSECS stations that most closely corresponded to acantharian collection sites. Resultant Ba/Sr distribution coefficients ( D Ba/Sr=( χ Ba/ χ Sr)/([Ba 2+] T/[Sr 2+] T)) in diverse areas of the world’s oceans are on the order of three or larger. These data, in conjunction with observations of acantharian mediated Sr 2+ depletions in the upper ocean, indicate that acantharians play a substantial role in the global oceanic Ba budget. Observation of Ba enrichments during celestite formation is consistent with expectations based on solidsolution–aqueous-solution precipitation dynamics and the much lower solubility of BaSO 4 compared to SrSO 4. Furthermore, the small solubility product of RaSO 4 relative to SrSO 4 and BaSO 4 indicates that Ra should be enriched in both celestite and barite. Consequently, acantharians may have a substantial influence on the oceanic distributions of both Ba and Ra.

Total amount of oceanic excess CO2 taken from the North Pacific subpolar region

Concentrations of total carbonate, alkalinity and dissolved oxygen were obtained near the 1973 GEOSECS stations in the North Pacific subpolar region north of 40°N along 175°E between 1993 and 1994. A difference of excess CO2 content between the GEOSECS and our expeditions was estimated. The maximum difference in water column inventory of excess CO2 has increased by about 280 gC m−2 above 2000 m depth which apparently means an uptake of excess CO2 taken from air to sea during the last two decades. An averaged value of the annual flux of excess CO2 at 75–1000 m depth was 8.63±2.01 gC m−2yr−1 in the North Pacific subpolar region. By introducing the annual flux of excess CO2 into a two-box model for the North Pacific subpolar region, a penetration factor of excess CO2 from air to sea was obtained to be 1.08×10−2 gC m−3ppm−1 in the North Pacific subpolar region. Based on this factor, the surface concentration of excess CO2 in the North Pacific subpolar region was estimated to be 68 μmole I−1, suggesting that the North Pacific subpolar region absorbed atmospheric excess CO2 more than the saturated concentration of excess CO2. Total amount of excess CO2 taken from the North Pacific subpolar region by 1993 was estimated to be 36.2×1015 gC, which was equal to about one tenth of that released by human activities after the preindustrial era.

Variability of the δ13C of dissolved inorganic carbon at a site in the north Pacific Ocean

We present a depth profile of δ 13 C- DIC (dissolved inorganic carbon) and a time-series of surface water δ 13 C- DIC from seawater samples collected at a single site during the Eve cruise in the North Pacific in June of 1987. Our deep water results confirm those reported by Kroopnick (1985) for GEOSECS Station 213 (10° west of Eve site). We observed a small but significant decrease in the δ 13 C of DIC in the upper 500 m of the water column over 13 years since the GEOSECS survey. This is likely due, at least in part, to the input of additional fossil fuel-derived CO 2 to the upper ocean. We observed a significant change in surface water δ 13 C over a short time period (2 days) that was the result of a change in the shallow surface water mass. This change emphasizes the need for caution when conducting seasonal studies.

The Inhomogeneous Distribution of Tritium and Radiocarbon in the Abyssal Southern Ocean

The tritium and radiocarbon measurements taken at the Southern Ocean GEOSECS stations were analyzed. Excess CO2 for the Atlantic GEOSECS stations 76,77,82,85,87,89,91 and for all the stations of the SOMOV-81 cruise were correlated with the radiotracer data. Radiocarbon and excess CO2 support the tritium data showing that these tracers are not homogeneously distributed in the deep-water column. The preformed radiocarbon value of the Antarctic Surface water component in the Antarctic Bottom Water was estimated to be-139.3×10^(-3).

210Po in the western Indian Ocean: distributions, disequilibria and partitioning between the dissolved and particulate phases

Seven GEOSECS stations in the western Indian Ocean were measured for dissolved 210Po, and five of these were also measured for particulate 210Po. Dissolved phase 210Po is lower than 210Pb in the deep water north of Madagascar, with values in the Arabian Sea being lower by about 4 dpm/100 kg (∼ 30%) for almost the entire water column. South of Madagascar, 210Po is essentially in equilibrium with 210Pb in the deep water, but with 210Po excess in subsurface water south of the Crozet basin. In the benthic boundary layer, 210Po is consistently lower than 210Pb for all the stations. In the particulate phase, 210Po shows a general increase with depth and is highest in the benthic boundary layer. In general, 210Po is lower than 210Pb in the particulate phase, but at the one Somali basin station where data are available, deep water 210Po is systematically higher than 210Pb. A mid-depth maximum of particulate 210Pb is generally associated with that of dissolved 210Pb. The partition of 210Po between the particulate and dissolved phases is not significantly different from that of 210Pb. The activities of the two nuclides in the particulate phase are generally less than 10% of those in the dissolved phase. The range is from 1% to 60%. High particulate and low dissolved activities are observed in the deep water, especially in the benthic boundary layer.

210Pb in the western Indian Ocean: distribution, disequilibrium, and partitioning between dissolved and particulate phases

Dissolved 210Pb profiles are presented for 13 GEOSECS stations in the western Indian Ocean. In surface water away from high southern latitudes, 210Pb is in excess over 226Ra due to the atmospheric fallout from decay of 222Rn. Except in the Circumpolar region, the dissolved 210Pb profiles display a gentle mid-depth maximum similar to the corresponding 226Ra profiles. The 210Pb/ 226Ra activity ratio ranges from 1.6 in the surface water east of Madagascar to 0.4 or less in the bottom water of all the basins. The lowest ratio observed was 0.1 in the Gulf of Aden very close to the continental land mass. A ratio of 0.6 divides the western Indian Ocean horizontally into two portions, with the contour at shallower depth in the north than in the south. The deep water disequilibrium is thus more extensive north of Madagascar than south of it. It appears that locality and bottom topography play a strong role in controlling the distributions of 210Pb and 226Ra as well as their extent of disequilibrium in the water column. The mean residence time for Pb with respect to particulate and boundary scavenging in the deep water ranges from about 15 to 75 years.

Intercomparison of 210Pb measurements at GEOSECS station 500 in the northeast Pacific

During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for 210Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured 210Pb results. The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%. The SIO experiments show that (1) the two scavenging methods employed (Fe(OH) 3 and Co-APDC co-precipitation) yield identical 210Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in 210Pb loss or contamination. The 210Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum 210Pb concentration around 500 m depth, marking the penetration depth of the flux of excess 210Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The 210Pb/ 226Ra activity ratio decreases monotonically from about 1 at the 210Pb minimum to about 0.5 near the bottom. The particulate 210Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate 210Pb profiles.

210Pb and 226Ra distributions in the Circumpolar waters

210Pb and 226Ra profiles have been measured at five GEOSECS stations in the Circumpolar region. These profiles show that 226Ra is quite uniformly distributed throughout the Circumpolar region, with slightly lower activities in surface waters, while 210Pb varies with depth as well as location or area. There is a subsurface 210Pb maximum which matches the oxygen minimum in depth and roughly correlates with the temperature and salinity maxima. This 210Pb maximum has its highest concentrations in the Atlantic sector and appears to originate near the South Sandwich Islands northeast of the Weddell Sea. Concentrations in this maximum decrease toward the Indian Ocean sector and then become fairly constant along the easterly Circumpolar Current. Relative to 226Ra, the activity of 210Pb is deficient in the entire water column of the Circumpolar waters. The deficiency increases from the depth of the 210Pb maximum toward the bottom, and the 210Pb/ 226Ra activity ratio is lowest in the Antarctic Bottom Water, indicating a rapid removal of Pb by particulate scavenging in the bottom layer and/or a short mean residence time of the Antarctic Bottom Water in the Circumpolar region. 226Ra is essentially linearly correlated with silica and barium in the Circumpolar waters. However, close examination of the vertical profiles reveals that Ba and Si are more variable than 226Ra in this region.