not for nothing since this post was from September but the call you are making on esri's elevation service is returning the depth/elev value in Web Mercator (the uom is meters not degrees) out in the polar regions along the Greenwich line.
Try this...
{
"objectId": 0,
"name": "Pixel",
"value": "730.826",
"location": {
"x": -1.107384508E7,
"y": 5054889.08,
"spatialReference": {
"wkid": 102100,
"latestWkid": 3857
}
},
"properties": null,
"catalogItems": null,
"catalogItemVisibilities": []
}
Identify: (WorldElevation/TopoBathy) (arcgis.com)