Halogen

This is a map based on the Cassini scenario from xkcd’s What if? series and takes place during southern hemisphere summer. My primary reference for this map was a climate model run by Nikolai Hersfeldt in ExoPlaSim and explored in his blog Worldbuilding Pasta. For anyone curious, I used Gimp, Photopea, Qgis, Gprojector, and Wilbur to create this map. Feel free to use this map for anything you like as long you give credit. The heightmap and individual layers are available upon request.

In my interpretation of this scenario, the change occurred sometime before the start of the Late Cenozoic Ice Age and the subsequent glaciation of Antarctica. As a result, the Laurentide ice sheet never formed, giving what would have been Canada and the Northern United States radically different geography. In the absence of Hudson Bay and the Great Lakes, there exists the Bell and St. Lawrence rivers. Prior to the onset of the Pleistocene glaciations, the Paleo Bell river may have drained an area larger than the Amazon basin and it survives to the modern day on Cassini Earth, forming a delta at the mouth of what would have been the Hudson Strait. Cassini Earth’s major ice sheets are thin and limited to the highlands of Tibet and the Andes, causing sea level to be around 70-76 meters higher, with some extra contribution from water displaced by uplifted regions and thermal expansion caused by higher average global temperatures. 

The Pacific Northwest is now both the hottest and driest place on the continent. However, the windward side of the Northern Rocky Mountains manage to capture some precipitation, supporting cloud forests and grasslands. Greenland and Iceland are almost entirely blanketed by tropical rainforests, though Greenland’s thins out to savanna and even a small patch of scrubland in the rain shadow of its highlands. The presence of North America and Eurasia directly to the north and south of the tropical Arctic Ocean forms a particularly strong monsoon pattern as Nikolai mentions in his blog, causing much of Canada to be drier than expected. Although Eastern Canada is dominated by savanna and scrubland, the Bell River is able to supply water across much of it and floods during the summer monsoon. The south east of the continent has a broadly similar climate, just flipped north to south. Quebec and New England are subtropical, the Midwest is still continental, and the Southern United States is subarctic and shrouded in conifers. Northern California is drier while the south is still predominantly Mediterranean. Baja California and Western Mexico resemble the old Pacific Northwest. Baja California receives the brunt of precipitation like our coastal Washington while partially insulating much of the Sonoran desert region. The Mexican highlands are now capped in ice sheets surrounded by mild tundra. During the winter, sea ice connects the islands of the Caribbean to one another as well as to Central America. 

Resources:

Climate Mini-Exploration: Checking Randall Munroe's Work

A new global ice sheet reconstruction for the past 80,000 years

GIS dataset of high-resolution rebound surfaces and ice-free paleotopography of glaciated North America since the LGM based on the ICE-xG (VMy) models' predictions

Earth2014: 1 arc-min shape, topography, bedrock and ice-sheet models

I forgot to post the Retrograde Eurasia map back when I finished it in February. Since we’re looking primarily at Asia and Europe this time, this map is by far the largest out of the five I’ve done. For any further details on the climate check out:

 https://www.reddit.com/r/worldbuilding/comments/1bwp6hn/v5_retrogradeclockwise_earth_map_and_accompanying/ 

I’ve been wanting to do a detailed tilted Antarctica map for a while now, but the low resolution of the bedmaps up until now and the need to reconstruct pre-glaciation topography made me a bit apprehensive to start it. However, the recent release of bedmap3 to the public gave me the motivation to give it a shot. For this map I used the isostatic adjustment from Paxman et al. (2022) on bedmap3 to create a version accounting for isostatic rebound. I then used the rasters of Antarctica during the Eocene-Oligocene boundary from reconstructions made by Paxman et al. (2019) and tried my best to combine it with my rebounded bedmap3 map, in order to preserve the fidelity of the highlands and add the features which were lost to erosion. I took this heightmap and ran it through Wilbur to carve out valleys and rivers as well as to add more detail to the coasts and ease the transition between the two maps. I then used the topography and likely climate of the continent to create a false satellite map. Finally, I looked up the names for various features, both glacial and subglacial to fill out the map. I also used qgis to help convert between projections and do raster calculations for the rebounded map.

Description:

It’s difficult to picture Antarctica as anything else aside from the vast frozen expanse we see at the bottom of the world today, but as with everything involving deep time, our present is only a snapshot in Earth’s history. Up until the Late Eocene, Antarctica was as rich and varied as any other landmass. From what little we have of Antarctica’s fossil record, its makeup was broadly similar to Pre-interchange South America, home to early Ungulates and Marsupials as well as their close relatives. Antarctica’s habitats were equally diverse, hosting grasslands and even Austral forests, likely resembling the Valdivian rainforests of Southern Chile, with even palms being present during the Paleogene. However, as South America and Australia departed northwards, the circumpolar-Antarctic current took hold, restricting the flow of warm subtropical waters to the poles. This cooled the continent and its elevated interior allowed glaciers to easily take hold, thereby dooming nearly all of its inhabitants to extinction. 

But what if this wasn’t its fate? Let's imagine that over the course of the last 40-45 million years, Earth’s poles slowly change their positions, slowly enough that its disruption to Earth’s climate is about as gradual as the movement of the continents. By the present, the North Pole is over Africa, somewhere in Northeast Nigeria, and the south pole over the middle of the Pacific, adjacent to the Manihiki islands, which places Antarctica squarely in the Tropics with the new equator running through East Antarctica. The tilt chosen for this map is the same as Jaredia from the World Dream Bank’s Planetocopia, an old website which depicted alternate versions of Earth, as well as alien planets. For now, we won’t focus on the ramifications this has for the rest of the planet. 

Being covered in glaciers over the last 34 million years has dramatically altered Antarctica’s topography, not only has the land been isostatically depressed, but the movement of glaciers has eroded vast tracts of the continent. This version of Antarctica never underwent any kind of extensive glaciation, resulting in a landmass quite alien compared to the one we would get if we simply removed the glaciers from Antarctica now. The Northeast of Antarctica is now covered in tropical rainforests, likely filled with a diverse array of marsupials and birds. Things become slightly drier as we travel inland and increase in elevation. Even without glaciers, much of the interior ranges from 1000-1300 meters above sea level, comparable to the South African Plateau; which now supports the world’s largest subtropical highlands, similar climatically to the highlands in Ethiopia. Much of the North-Eastern side of the highlands drains into the Lambert graben, a permian-aged rift, which now forms a bay. Rivers coming down from the highlands introduce an immense amount of water into the bay, making the majority of the bay range from fresh to brackish, and with the sediment supplied by the mountains making this bay rather shallow. During Glacial maximums, this bay transforms into a low-lying plain, the sediment of which now makes the seabed ample territory for seagrass meadows. Further into the highlands, we find Lake Vostok, now relieved of its burden of ice. Without the depression from the ice above, the coasts of lake Vostok sit at about 1000 meters above sea level and are surrounded by subtropical forests. The lake’s depths nearly extend back down to sea level, supporting hydrothermal vents like those in Lake Baikal, with the only indication that something is different being the new flow of detritus from above. 

To the West we find a desert encompassing almost all of Marie Byrd Land and the Southern portion of the Palmer Peninsula. Sediment derived from the Marie Byrd land volcanic field, dispersed by the winds, colors vast swaths of the desert red. A few of the shield volcanoes in the Marie Byrd Land volcanic province rise high enough to capture some moisture, creating small oases of highland grasslands and in rare cases cloud forests. The Northern tropical forests of the Palmer peninsula are uniquely isolated from the mainland by Ronne bay to the East and the West Antarctic desert to the south, meaning any fauna here would likely be endemic to it. In the Ross Bay, the Transantarctic mountains cast a sizable rain shadow to the west, helping to form a narrow desert on the leeward side. In Ross bay, we also find a small archipelago of desert islands, with the largest being Penwell Island, a remnant of which exists in our Antarctica as Penwell Bank. To the South we reach the boundary between the tropics and subtropics. Near Antarctica’s new southernmost point we find the mouth of the Wilke’s river: the longest river on the Antarctic continent and which terminates with a wave-dominated delta. It’s also here that we find the largest permanent glacier on the continent, limited only to the highest points of the Victory Mountains.

Even without the circumpolar Antarctic current, Antarctica remains an extremely isolated landmass. No land bridges have connected it to any other continent since the Eocene, though South America (Now north of North America) remains just within reach. Ocean currents in the Drake Passage travel primarily from East to west, meaning that rafting events are unlikely to take settlers from South America to Australia, but could take settlers the other way around. It’s possible that South America could receive a regular influx of marsupials and other fauna from Antarctica over the course of millions of years. 

Resources Used:

Bedmap3: https://data.bas.ac.uk/full-record.php?id=GB/NERC/BAS/PDC/01615 

Reconstructions of Antarctic topography since the Eocene–Oligocene boundary: https://doi.org/10.1016/j.palaeo.2019.109346 

Retrograde North America (North America on a backwards rotating Earth):

Retrograde South America

This is my attempt to emulate a satellite map of South America on a backward spinning Earth, I based this on the climate maps made by Molotovsnowman and AncalagonTheBlack42: https://www.deviantart.com/molotovjack/art/Retrograde-Earth-V5-Final-Version-985503973

Which themselves were based on this study and this map from the Worldbuilding Pasta Blog

https://esd.copernicus.org/articles/9/1191/2018/

Tilted Africa