13D Filing: Mangrove Partners and Atlantic Power Corp (AT)

The following constitutes
Amendment No. 4 to the Schedule 13D filed by the undersigned (“Amendment No. 4”). This Amendment No. 4 amends the Schedule
13D as specifically set forth herein.

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended
and restated to read as follows:

The 11,324,092 Shares
directly owned by Mangrove Master Fund were purchased with working capital (which may, at any given time, include margin loans
made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted, as set forth in
Schedule B annexed hereto (“Schedule B”). The aggregate purchase price of the 11,324,092 Shares directly
owned by Mangrove Master Fund is, in U.S. dollar terms, approximately $25,341,663, including brokerage commissions.

Item 5.

Interest in Securities of the Issuer.

Items 5(a)-(c) are
hereby amended and restated to read as follows:

The aggregate percentage
of Shares reported owned by each person named herein is based upon 115,229,497 Shares outstanding as of May 2, 2017, which is the
total number of Shares outstanding as reported in the Issuer’s Form 10-Q filed with the Securities and Exchange Commission
on May 4, 2017.

A.

Mangrove Master Fund

(a)

As of the close of business on July 21, 2017, Mangrove Master Fund directly owned 11,324,092 Shares.

Percentage: Approximately 9.8%

(b)

1. Sole power to vote or direct vote: 0 2. Shared power to vote or direct vote: 11,324,092 3. Sole power to dispose or direct the disposition: 0 4. Shared power to dispose or direct the disposition: 11,324,092

(c)

The transactions in the Shares by Mangrove Master Fund during the past sixty (60) days are set forth in Schedule B and are incorporated herein by reference.

B.

Mangrove Fund

(a)

As of the close of business on July 21, 2017, Mangrove Fund, as a controlling shareholder of Mangrove Master Fund, may be deemed to beneficially own the 11,324,092 Shares directly owned by Mangrove Master Fund.

Percentage: Approximately 9.8%