3. Water mass distribution maps

From the gridded T/S analyses for the 1950–1994 and IPY periods, water mass properties reveal qualitative differences between them. The use of density-related properties to distinguish water masses is less certain than chemical analysis [22, 34]. Scarcity of widespread chemical tracer surveys precludes such an approach here, and analysis based on the more common T/S data is adopted. This work chooses to map Atlantic water (AW) and summer Pacific water (SPW) for both their simplicity of definition and importance in the freshwater (FW) and thermal budget of the AO. Characteristics used to identify AW and SPW are adapted from [25] and [35, 36], respectively, and are described below.

The AW distinguishes an intermediate layer of warm water of Atlantic origin that has entered the Arctic Basin through deep coastal channels and bathymetric steering. Over-basin AW typically has S ≥ 34.8 PSU with T ≥ 0°C despite heat loss along the Eurasian shelf. SPW denotes relatively fresh waters with 31 PSU ≤ S ≤ 33 PSU and T ≥ 1.4°C entering the AO through the Bering Strait which have cooled after residence on the shallow Chukchi Shelf and include substantial meteoric FW [21, 35]. These low-density waters form a subsurface layer in the western Arctic typically at depths between 50 and 100 m and often include a local temperature maximum [37, 38].

In Figures 1–11, left-side plots show the identified field for the IPY dataset, while the right-side plot shows the corresponding anomaly field relative to the

Russian 1950–1994 archive. We refer to each such pair singularly as a figure and distinguish between the field and its anomaly in context. Figure 1 maps the 34.8 PSU isohaline depth. Figure 2 shows the integrated FW content (FWC), in meters

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic…

Figures 3–7 plot the AW core depth, core temperature, heat content, lower boundary depth, and upper boundary depth, respectively. AW here is defined as waters composing a continuous vertical region of positive temperature bounded by 0°C isotherms, which define herein the lower and upper AW boundary depths. The AW core depth and temperature are adopted to be the depth and value of the

of freshwater, with respect to 34.8 PSU.

AW core depth. IPY (l) and anomaly (r).

FWC relative to 34.8 PSU isohaline. IPY (l) and anomaly (r).

DOI: http://dx.doi.org/10.5772/intechopen.80926

Figure 2.

Figure 3.

9

Figure 1. 34.8 PSU isohaline depth. IPY (l) and anomaly (r).

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic… DOI: http://dx.doi.org/10.5772/intechopen.80926

Figure 2. FWC relative to 34.8 PSU isohaline. IPY (l) and anomaly (r).

Russian 1950–1994 archive. We refer to each such pair singularly as a figure and distinguish between the field and its anomaly in context. Figure 1 maps the 34.8 PSU isohaline depth. Figure 2 shows the integrated FW content (FWC), in meters of freshwater, with respect to 34.8 PSU.

Figures 3–7 plot the AW core depth, core temperature, heat content, lower boundary depth, and upper boundary depth, respectively. AW here is defined as waters composing a continuous vertical region of positive temperature bounded by 0°C isotherms, which define herein the lower and upper AW boundary depths. The AW core depth and temperature are adopted to be the depth and value of the

the gridding. Bathymetric masking was inferred from the International Bathymetric Chart of the Arctic Ocean [33], and regions with depth less than 200 m are masked. The correlation length scales for observations correspond to three grid cells with a signal-to-noise ratio of 10%. The same procedure applied to historical observations collected during 1950–1994 (privately archived at the Arctic and Antarctic Research Institute of Russia) generates mean climate dataset for that period, which is used to

From the gridded T/S analyses for the 1950–1994 and IPY periods, water mass properties reveal qualitative differences between them. The use of density-related properties to distinguish water masses is less certain than chemical analysis [22, 34]. Scarcity of widespread chemical tracer surveys precludes such an approach here, and analysis based on the more common T/S data is adopted. This work chooses to map Atlantic water (AW) and summer Pacific water (SPW) for both their simplicity of definition and importance in the freshwater (FW) and thermal budget of the AO. Characteristics used to identify AW and SPW are adapted from [25] and

The AW distinguishes an intermediate layer of warm water of Atlantic origin that has entered the Arctic Basin through deep coastal channels and bathymetric steering. Over-basin AW typically has S ≥ 34.8 PSU with T ≥ 0°C despite heat loss along the Eurasian shelf. SPW denotes relatively fresh waters with 31 PSU ≤ S ≤ 33 PSU and T ≥ 1.4°C entering the AO through the Bering Strait which have cooled after residence on the shallow Chukchi Shelf and include substantial meteoric FW [21, 35]. These low-density waters form a subsurface layer in the western Arctic typically at depths between 50 and 100 m and often include a local temperature

In Figures 1–11, left-side plots show the identified field for the IPY dataset, while the right-side plot shows the corresponding anomaly field relative to the

contrast the gridded IPY data.

maximum [37, 38].

Figure 1.

8

34.8 PSU isohaline depth. IPY (l) and anomaly (r).

3. Water mass distribution maps

Arctic Studies - A Proxy for Climate Change

[35, 36], respectively, and are described below.

Figure 4. AW core temperature. IPY (l) and anomaly (r).

### Figure 5. AW heat content. IPY (l) and anomaly (r).

temperature maximum within the AW layer. Total heat content is calculated as the vertical integral of specific heat with respect to 1.8°C between AW boundaries.

occurring below the surface mixed layer within the salinity range 30.5–33.0 PSU [35]. Upper and lower SPW boundary depths are determined T ≥ 1.4°C and salinity restriction to that range. Figure 8 maps the depth of the maximum temperature found in SPW, and Figure 9 identifies these maxima. Figures 10 and 11 show

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic…

the lower and upper boundary depths of SPW.

AW upper boundary. IPY (l) and anomaly (r).

Figure 6.

Figure 7.

11

AW lower boundary. IPY (l) and anomaly (r).

DOI: http://dx.doi.org/10.5772/intechopen.80926

Insufficient deep data in near the Canadian Archipelago precludes a resolution of the AW lower boundary and consequently of the heat content in that area.

Figures 8–11 show calculated fields for summer Pacific water, which exists only on the Pacific side of the Arctic. SPW is defined by a local temperature maximum

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic… DOI: http://dx.doi.org/10.5772/intechopen.80926

Figure 6. AW lower boundary. IPY (l) and anomaly (r).

Figure 7. AW upper boundary. IPY (l) and anomaly (r).

occurring below the surface mixed layer within the salinity range 30.5–33.0 PSU [35]. Upper and lower SPW boundary depths are determined T ≥ 1.4°C and salinity restriction to that range. Figure 8 maps the depth of the maximum temperature found in SPW, and Figure 9 identifies these maxima. Figures 10 and 11 show the lower and upper boundary depths of SPW.

temperature maximum within the AW layer. Total heat content is calculated as the vertical integral of specific heat with respect to 1.8°C between AW boundaries. Insufficient deep data in near the Canadian Archipelago precludes a resolution

Figures 8–11 show calculated fields for summer Pacific water, which exists only on the Pacific side of the Arctic. SPW is defined by a local temperature maximum

of the AW lower boundary and consequently of the heat content in that area.

Figure 4.

Figure 5.

10

AW heat content. IPY (l) and anomaly (r).

AW core temperature. IPY (l) and anomaly (r).

Arctic Studies - A Proxy for Climate Change

### Figure 8.

Summer PW depth of Tmax. IPY (l) and anomaly (r).

4. Changes inferred from T/S observations

Summer PW upper boundary depth. IPY (l) and anomaly (r).

DOI: http://dx.doi.org/10.5772/intechopen.80926

articles/arctic-ocean-features/.

4.1 Atlantic waters

Figure 11.

ice-related processes [40].

13

In general, the vertical and spatial patterns of hydrographic parameters in the

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic…

Elevated pan-Arctic heat content due to the extraordinary heat transported to the AO from the North Atlantic is a significant change evident during the IPY period. Advection of relatively warmer AW resulted in anomalous hydrographic state formation over the entire deep Arctic Basin [17, 38]. The temperatures within the core of AW were observed 0.3–1.0°C higher than climatic values; mean changes are 0.65°C over the Eurasian Basin and 0.25°C over Canada and Makarov basins. Of further note is the warm tongue of AW that appears to be topographically steered by the Lomonosov Ridge; Figure 4 shows a clear 0.5°C core temperature anomalous increase extending from the Laptev Sea toward the Greenland Shelf. This feature resides at a depth of about 275 m, 75 m surfaceward of the historic AW core depth per Figure 3. Over the Makarov Basin, AW expanded 50 m deep into the column [39], while the AW core depth has moved 100–150 m surfaceward with an associated 0.5–1.0 GJ/m<sup>2</sup> increase in associated heat content. Similar changes including the AW moving surfaceward and retaining more heat at depth are present throughout most of the AO indicating stronger potential influence on

By 2007, the intermediate AW layer had deepened and thickened in the Pacific sector [23], but the changes are heterogeneous over the central and Eurasian basins.

AO and adjacent North Atlantic had undergone considerable changes by IPY although the large-scale distributions of the water masses align with the historic climatology. Readers unfamiliar with AO geography and its bathymetric features are encouraged to follow this discussion with an atlas, e.g. https://geology.com/

Figure 9. Summer PW Tmax. IPY (l) and anomaly (r).

Figure 10. Summer PW lower boundary depth. IPY (l) and anomaly (r).

Changes in Arctic Ocean Climate Evinced through Analysis of IPY 2007–2008 Oceanographic… DOI: http://dx.doi.org/10.5772/intechopen.80926

Figure 11. Summer PW upper boundary depth. IPY (l) and anomaly (r).
