Abstract:We use new observations of stable water isotopes from a research cruise in early 2017 to highlight ocean‐ice interactions occurring under Filchner‐Ronne Ice Shelf, the largest Antarctic ice shelf. In particular, we investigate the properties of Ice Shelf Water with temperature lower than the surface freezing point, in the Filchner Depression. We identify two main flavors of Ice Shelf Water emerging from beneath the Filchner Ice Shelf, which originate from High Salinity Shelf Water end members with distinct cha… Show more
“…Based on measurements from the same drill holes as discussed above (Figure 1), Huhn et al (2018) report neon-based GBMW baseline fractions of 1.0%-3.6% directly at the FIS base, and lower fractions of <0.4% near the bottom of the northern FIS and in Filchner Trough in 2016. These values are consistent with the (stable oxygen isotopes-based) fractions of 0.4% in Filchner Trough in 2017 reported by Akhoudas et al (2020). In 2018, the FIS front was dominated by ISW, coincident with the highest water mass age (Figure 9) and elevated GBMW fractions of 0.8%-1.0% below a depth of 600 m. These fractions directly agree with the fractions measured by Huhn et al (2018, see their Figure 3) at the northern FIS drill hole sites.…”
Section: On the Hydrographic Transition Between 2017 And 2018 At The Fis Frontsupporting
confidence: 92%
“…The 2018-conditions contrast with those observed one year earlier in 2017, when a CTD and stable isotope tracer survey found that Berkner HSSW-sourced ISW dominated in Filchner Trough (Akhoudas et al, 2020). These two different hydrographic conditions are referred to as Berkner-and Ronne-modes, and are mainly manifested by contrasting hydrographic conditions underneath the northern FIS and in Filchner Trough, as schematically illustrated in Figure 11.…”
Section: On the Hydrographic Transition Between 2017 And 2018 At The Fis Frontmentioning
The Antarctic continent stores the largest amount of freshwater on Earth. However, the Antarctic ice sheets and glaciers are losing mass, leading to a cumulative sea level rise of 14 mm since 1979 (Rignot et al., 2019). Some ice mass loss could be linked to changes in the atmosphere, such as the warming of the Antarctic Peninsula (Vaughan et al., 2003), which triggered the decay of the Larsen ice shelves (Broeke, 2005;Rott et al., 1996). However, the majority of ice mass was lost from glaciers and ice sheets that were exposed to the influence of warm ocean waters (Rignot et al., 2019). Thompson et al. (2018) classify the Antarctic
“…Based on measurements from the same drill holes as discussed above (Figure 1), Huhn et al (2018) report neon-based GBMW baseline fractions of 1.0%-3.6% directly at the FIS base, and lower fractions of <0.4% near the bottom of the northern FIS and in Filchner Trough in 2016. These values are consistent with the (stable oxygen isotopes-based) fractions of 0.4% in Filchner Trough in 2017 reported by Akhoudas et al (2020). In 2018, the FIS front was dominated by ISW, coincident with the highest water mass age (Figure 9) and elevated GBMW fractions of 0.8%-1.0% below a depth of 600 m. These fractions directly agree with the fractions measured by Huhn et al (2018, see their Figure 3) at the northern FIS drill hole sites.…”
Section: On the Hydrographic Transition Between 2017 And 2018 At The Fis Frontsupporting
confidence: 92%
“…The 2018-conditions contrast with those observed one year earlier in 2017, when a CTD and stable isotope tracer survey found that Berkner HSSW-sourced ISW dominated in Filchner Trough (Akhoudas et al, 2020). These two different hydrographic conditions are referred to as Berkner-and Ronne-modes, and are mainly manifested by contrasting hydrographic conditions underneath the northern FIS and in Filchner Trough, as schematically illustrated in Figure 11.…”
Section: On the Hydrographic Transition Between 2017 And 2018 At The Fis Frontmentioning
The Antarctic continent stores the largest amount of freshwater on Earth. However, the Antarctic ice sheets and glaciers are losing mass, leading to a cumulative sea level rise of 14 mm since 1979 (Rignot et al., 2019). Some ice mass loss could be linked to changes in the atmosphere, such as the warming of the Antarctic Peninsula (Vaughan et al., 2003), which triggered the decay of the Larsen ice shelves (Broeke, 2005;Rott et al., 1996). However, the majority of ice mass was lost from glaciers and ice sheets that were exposed to the influence of warm ocean waters (Rignot et al., 2019). Thompson et al. (2018) classify the Antarctic
“…During this period, observed source water salinities (Methods) between 34.84 g kg −1 (34.65 psu) and 34.87 g kg −1 (34.7 psu) at FNE1 and FNE2 (Fig. 2c ) compare well with the Berkner HSSW 21 , 26 that is found on the shallow continental shelf between the Filchner and Ronne ice shelves north of Berkner Island 27 . Fig.…”
Section: Resultsmentioning
confidence: 61%
“…Neglecting minor corrections due to heat conduction at the ice–ocean interface, the slope of these lines is given as , with specific heat capacity of seawater J kg −1 K −1 and latent heat of fusion J kg −1 and salinity of the seawater that is being in contact with the ice. In particular, in absence of other freshwater sources or T–S end-members, Gade-line theory can be used to invert for the open ocean water mass type that has been the source water for a given ISW type, as e.g., done by 26 to discriminate between Berkner HSSW and Ronne HSSW source water types for FRIS ISW. Assuming that ISW being observed at the mooring sites originated from HSSW on the continental shelf, the “source water salinity” of this HSSW is found as the intersection of the ISW’s Gade-line with the surface freezing point temperature.…”
Floating ice shelves are the Achilles’ heel of the Antarctic Ice Sheet. They limit Antarctica’s contribution to global sea level rise, yet they can be rapidly melted from beneath by a warming ocean. At Filchner-Ronne Ice Shelf, a decline in sea ice formation may increase basal melt rates and accelerate marine ice sheet mass loss within this century. However, the understanding of this tipping-point behavior largely relies on numerical models. Our new multi-annual observations from five hot-water drilled boreholes through Filchner-Ronne Ice Shelf show that since 2015 there has been an intensification of the density-driven ice shelf cavity-wide circulation in response to reinforced wind-driven sea ice formation in the Ronne polynya. Enhanced southerly winds over Ronne Ice Shelf coincide with westward displacements of the Amundsen Sea Low position, connecting the cavity circulation with changes in large-scale atmospheric circulation patterns as a new aspect of the atmosphere-ocean-ice shelf system.
“…3A). On the continental shelf in the Filchner Depression (75-78 S), the 28.37 kg m 3 g n surface is associated with very depleted d 18 O values, as a result of the influence of glacial meltwater in this region36 . As this water-mass flows out along the continental slope following the clockwise circulation of the gyre, it quickly loses its d 18 O signature(Fig.…”
The Atlantic sector of the Southern Ocean is the world’s main production site of Antarctic Bottom Water, a water-mass that is ventilated at the ocean surface before sinking and entraining older water-masses – ultimately replenishing the abyssal global ocean. In recent decades, numerous attempts at estimating the rates of ventilation and overturning of Antarctic Bottom Water in this region have led to a strikingly broad range of results, with water transport-based calculations (8.4-9.7 Sv) yielding larger rates than tracer-based estimates (3.7-4.9 Sv). Here, we reconcile these conflicting views by integrating transport- and tracer-based estimates within a common analytical framework, in which bottom water formation processes are explicitly quantified. We show that the layer of Antarctic Bottom Water denser than 28.35 kg m−3 γn is exported northward at a rate of 8.7 ± 0.9 Sv, composed of 4.8 ± 1.3 Sv of well-ventilated Dense Shelf Water, and 3.9 ± 1.1 Sv of old Circumpolar Deep Water entrained into cascading plumes. The majority, but not all, of the Dense Shelf Water (3.5 ± 2.7 Sv) is generated on the continental shelves of the Weddell Sea. Only 55% of AABW exported from the region are well ventilated thus participating to heat and carbon uptake in the deep ocean, and in the Weddell sector, entrainment of older waters occurs at a ratio of 2.1 ± 0.8. Our findings unify traditionally contrasting views of Antarctic Bottom Water production in the Atlantic sector, and define a baseline, process-discerning target for its realistic representation in climate models.
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